Provided by: multipath-tools_0.8.8-1ubuntu1.22.04.4_amd64 bug

NAME

       multipath.conf - multipath daemon configuration file.

DESCRIPTION

       /etc/multipath.conf  is  the  configuration  file  for the multipath daemon. It is used to
       overwrite the built-in configuration table of multipathd.  Any line whose first non-white-
       space character is a '#' is considered a comment line. Empty lines are ignored.

       Currently  used  multipathd  configuration  can  be  displayed  with  the  multipath -t or
       multipathd show config command.

SYNTAX

       The configuration file contains entries of the form:

              <section> {
                     <attribute> <value>
                     ...
                     <subsection> {
                            <attribute> <value>
                            ...
                     }
              }

       Each section contains one or more attributes or subsections. The recognized  keywords  for
       attributes or subsections depend on the section in which they occur.

       <attribute>  and  <value>  must  be  on a single line.  <attribute> is one of the keywords
       listed in this man page.  <value> is either a simple word (containing  no  whitespace  and
       none of the characters '"', '#', and '!') or one string enclosed in double quotes ("...").
       Outside a quoted string, text starting with '#', and '!' is  regarded  as  a  comment  and
       ignored  until  the  end  of  the  line.  Inside  a  quoted string, '#' and '!' are normal
       characters, and whitespace is preserved.  To represent a double quote character  inside  a
       double  quoted  string,  use  two consecutive double quotes ('""'). Thus '2.5" SSD' can be
       written as "2.5"" SSD".

       Opening braces ('{') must follow the (sub)section name on the same  line.  Closing  braces
       ('}') that mark the end of a (sub)section must be the only non-whitespace character on the
       line. Whitespace is ignored except inside double quotes, thus the indentation shown in the
       above example is helpful for human readers but not mandatory.

       Note  on regular expressions: The multipath.conf syntax allows many attribute values to be
       specified as POSIX Extended Regular Expressions (see regex(7)). These regular  expressions
       are  case  sensitive  and  not  anchored,  thus  the  expression  "bar"  matches "barbie",
       "rhabarber", and "wunderbar", but not  "Barbie".  To  avoid  unwanted  substring  matches,
       standard regular expression syntax using the special characters "^" and "$" can be used.

       The following section keywords are recognized:

       defaults         This  section  defines  default  values  for  attributes  which  are used
                        whenever no values are given  in  the  appropriate  device  or  multipath
                        sections.

       blacklist        This  section defines which devices should be excluded from the multipath
                        topology discovery.

       blacklist_exceptions
                        This section defines which devices should be included  in  the  multipath
                        topology discovery, despite being listed in the blacklist section.

       multipaths       This  section  defines  the  multipath  topologies. They are indexed by a
                        World Wide Identifier(WWID). For  details  on  the  WWID  generation  see
                        section  WWID  generation  below.  Attributes  set  in  this section take
                        precedence over all others.

       devices          This section defines the device-specific settings. Devices are identified
                        by vendor, product, and revision.

       overrides        This  section  defines  values  for  attributes  that should override the
                        device-specific settings for all devices.

defaults section

       The defaults section recognizes the following keywords:

       verbosity        Default verbosity. Higher values  increase  the  verbosity  level.  Valid
                        levels are between 0 and 6.

                        The default is: 2

       polling_interval Interval  between  two  path  checks in seconds. For properly functioning
                        paths,  the  interval  between  checks   will   gradually   increase   to
                        max_polling_interval.   This  value will be overridden by the WatchdogSec
                        setting in the multipathd.service definition if systemd is used.

                        The default is: 5

       max_polling_interval
                        Maximal interval between two path checks in seconds.

                        The default is: 4 * polling_interval

       reassign_maps    Enable reassigning of device-mapper maps.  With  this  option  multipathd
                        will  remap  existing  device-mapper  maps  to  always point to multipath
                        device, not the underlying block devices. Possible values are yes and no.

                        The default is: no

       multipath_dir    This option is deprecated, and will  be  removed  in  a  future  release.
                        Directory where the dynamic shared objects are stored. Defined at compile
                        time, commonly /lib64/multipath/ or /lib/multipath/.

                        The default is: <system dependent>

       path_selector    The default path selector algorithm to  use;  they  are  offered  by  the
                        kernel multipath target:

                        round-robin 0
                                    Loop  through  every path in the path group, sending the same
                                    amount of I/O to  each.  Some  aspects  of  behavior  can  be
                                    controlled  with  the attributes: rr_min_io, rr_min_io_rq and
                                    rr_weight.

                        queue-length 0
                                    (Since 2.6.31 kernel) Choose the path for the next  bunch  of
                                    I/O based on the amount of outstanding I/O to the path.

                        service-time 0
                                    (Since  2.6.31  kernel) Choose the path for the next bunch of
                                    I/O based on the amount of outstanding I/O to  the  path  and
                                    its relative throughput.

                        historical-service-time 0
                                    (Since  5.8 kernel) Choose the path for the next bunch of I/O
                                    based on the estimation of future service time based  on  the
                                    history of previous I/O submitted to each path.

                        io-affinity 0
                                    (Since 5.11 kernel) Choose the path for the next bunch of I/O
                                    based on a CPU to path mapping the user passes  in  and  what
                                    CPU we are executing on.

                        The default is: service-time 0

       path_grouping_policy
                        The  default  path  grouping  policy  to apply to unspecified multipaths.
                        Possible values are:

                        failover    One path per priority group.

                        multibus    All paths in one priority group.

                        group_by_serial
                                    One priority group per serial number.

                        group_by_prio
                                    One  priority  group  per  priority  value.  Priorities   are
                                    determined  by  callout  programs specified as a global, per-
                                    controller or per-multipath option in the configuration file.

                        group_by_node_name
                                    One priority group per target node name.  Target  node  names
                                    are fetched in /sys/class/fc_transport/target*/node_name.

                        The default is: failover

       uid_attrs        Setting  this option activates merging uevents by WWID, which may improve
                        uevent processing effiency.  Moreover,  it's  an  alternative  method  to
                        configure  the  udev  properties  to  use  for  determining  unique  path
                        identifiers (WWIDs).

                        The value of this option is  a  space  separated  list  of  records  like
                        "type:ATTR",  where  type  is matched against the beginning of the device
                        node name (e.g. sd:ATTR matches sda), and ATTR is the name  of  the  udev
                        property to use for matching devices.

                        If  this  option  is  configured  and  matches  the device node name of a
                        device, it overrides any other configured  methods  for  determining  the
                        WWID for this device.

                        The  default  is:  <unset>.  To  enable  uevent  merging,  set it e.g. to
                        "sd:ID_SERIAL dasd:ID_UID nvme:ID_WWN".

       uid_attribute    The  udev  attribute  providing  a  unique  path  identifier  (WWID).  If
                        uid_attribute  is  set  to  the  empty string, WWID determination is done
                        using the sysfs  method  rather  then  using  udev  (not  recommended  in
                        production; see WWID generation below).

                        The default is: ID_SERIAL, for SCSI devices

                        The default is: ID_UID, for DASD devices

                        The default is: ID_WWN, for NVMe devices

       getuid_callout   (Superseded  by uid_attribute) The default program and args to callout to
                        obtain a unique path identifier. Should be  specified  with  an  absolute
                        path.

                        The default is: <unset>

       prio             The  name  of  the  path  priority  routine. The specified routine should
                        return a numeric value specifying the relative  priority  of  this  path.
                        Higher number have a higher priority.  "none" is a valid value. Currently
                        the following path priority routines are implemented:

                        const       Return a constant priority of 1.

                        sysfs       Use the sysfs attributes access_state and  preferred_path  to
                                    generate  the  path  priority.  This  prioritizer accepts the
                                    optional prio_arg exclusive_pref_bit.

                        emc         (Hardware-dependent) Generate the path priority for DGC class
                                    arrays as CLARiiON CX/AX and EMC VNX and Unity families.

                        alua        (Hardware-dependent)  Generate the path priority based on the
                                    SCSI-3 ALUA settings. This prioritizer accepts  the  optional
                                    prio_arg exclusive_pref_bit.

                        ontap       (Hardware-dependent)  Generate  the  path priority for NetApp
                                    ONTAP class and OEM arrays as IBM NSeries.

                        rdac        (Hardware-dependent)   Generate   the   path   priority   for
                                    LSI/Engenio/NetApp  RDAC  class  as  NetApp  SANtricity  E/EF
                                    Series, and OEM arrays from IBM DELL SGI STK and SUN.

                        hp_sw       (Hardware-dependent)   Generate   the   path   priority   for
                                    HP/COMPAQ/DEC  HSG80  and  MSA/HSV arrays with Active/Standby
                                    mode exclusively.

                        hds         (Hardware-dependent) Generate the path priority  for  Hitachi
                                    AMS families of arrays other than AMS 2000.

                        random      Generate a random priority between 1 and 10.

                        weightedpath
                                    Generate  the  path  priority based on the regular expression
                                    and the priority provided  as  argument.  Requires  prio_args
                                    keyword.

                        path_latency
                                    Generate  the  path  priority  based  on a latency algorithm.
                                    Requires prio_args keyword.

                        ana         (Hardware-dependent) Generate the path priority based on  the
                                    NVMe ANA settings.

                        datacore    (Hardware-dependent)  Generate  the  path  priority  for some
                                    DataCore storage arrays. Requires prio_args keyword.

                        iet         (iSCSI only) Generate path priority for iSCSI  targets  based
                                    on IP address. Requires prio_args keyword.

                        The  default  depends  on  the detect_prio setting: If detect_prio is yes
                        (default), the default priority algorithm is sysfs (except for NetAPP  E-
                        Series,  where  it  is  alua). If detect_prio is no, the default priority
                        algorithm is const.

       prio_args        Arguments to pass to to the prio function. This only applies  to  certain
                        prioritizers:

                        weighted    Needs a value of the form "<hbtl|devname|serial|wwn> <regex1>
                                    <prio1> <regex2> <prio2> ..."

                                    hbtl    Regex can be of SCSI  H:B:T:L  format.  For  example:
                                            1:0:.:. , *:0:0:.

                                    devname Regex  can be of device name format. For example: sda
                                            , sd.e

                                    serial  Regex can be of serial number  format.  For  example:
                                            .*J1FR.*324  .  The  serial  can be looked up through
                                            sysfs or by  running  multipathd  show  paths  format
                                            "%z". For example: 0395J1FR904324

                                    wwn     Regex       can       be       of       the      form
                                            "host_wwnn:host_wwpn:target_wwnn:target_wwpn"   these
                                            values  can  be looked up through sysfs or by running
                                            multipathd  show  paths  format  "%N:%R:%n:%r".   For
                                            example:  0x200100e08ba0aea0:0x210100e08ba0aea0:.*:.*
                                            , .*:.*:iqn.2009-10.com.redhat.msp.lab.ask-06:.*

                        path_latency
                                    Needs a value of the form "io_num=<20> base_num=<10>"

                                    io_num  The number of read  IOs  sent  to  the  current  path
                                            continuously,  used  to  calculate  the  average path
                                            latency.  Valid Values: Integer, [2, 200].

                                    base_num
                                            The base number value of logarithmic scale,  used  to
                                            partition  different  priority  ranks.  Valid Values:
                                            Integer, [2, 10]. And Max average  latency  value  is
                                            100s, min average latency value is 1us.  For example:
                                            If base_num=10, the paths will be grouped in priority
                                            groups  with  path latency <=1us, (1us, 10us], (10us,
                                            100us], (100us, 1ms],  (1ms,  10ms],  (10ms,  100ms],
                                            (100ms, 1s], (1s, 10s], (10s, 100s], >100s.

                        alua        If  exclusive_pref_bit  is set, paths with the preferred path
                                    bit set will always be in their own path group.

                        sysfs       If exclusive_pref_bit is set, paths with the  preferred  path
                                    bit set will always be in their own path group.

                        datacore

                                    preferredsds
                                            (Mandatory) The preferred "SDS name".

                                    timeout (Optional) The timeout for the INQUIRY, in ms.

                        iet

                                    preferredip=...
                                            (Mandatory)   Th  preferred  IP  address,  in  dotted
                                            decimal notation, for iSCSI targets.

                        The default is: <unset>

       features         Specify any device-mapper features to be used. Syntax is num  list  where
                        num is the number, between 0 and 8, of features in list.  Possible values
                        for the feature list are:

                        queue_if_no_path
                                    (Deprecated, superseded by no_path_retry)  Queue  I/O  if  no
                                    path  is  active.   Identical to the no_path_retry with queue
                                    value. If both this feature and no_path_retry  are  set,  the
                                    latter value takes precedence. See KNOWN ISSUES.

                        pg_init_retries <times>
                                    (Since  kernel  2.6.24)  Number of times to retry pg_init, it
                                    must be between 1 and 50.

                        pg_init_delay_msecs <msecs>
                                    (Since kernel 2.6.38) Number of msecs before  pg_init  retry,
                                    it must be between 0 and 60000.

                        queue_mode <mode>
                                    (Since kernel 4.8) Select the the queueing mode per multipath
                                    device.  <mode> can be bio, rq or mq,  which  corresponds  to
                                    bio-based,   request-based,   and  block-multiqueue  (blk-mq)
                                    request-based, respectively.   The  default  depends  on  the
                                    kernel parameter dm_mod.use_blk_mq. It is mq if the latter is
                                    set, and rq otherwise.

                        The default is: <unset>

       path_checker     The default method used to determine the path's  state.  The  synchronous
                        checkers  (all  except  tur  and directio) will cause multipathd to pause
                        most activity, waiting up to checker_timeout  seconds  for  the  path  to
                        respond.  The  asynchronous  checkers  (tur  and directio) will not pause
                        multipathd. Instead, multipathd  will  check  for  a  response  once  per
                        second, until checker_timeout seconds have elapsed. Possible values are:

                        readsector0 (Deprecated)  Read  the  first  sector  of  the  device. This
                                    checker is being deprecated, please use tur instead.

                        tur         Issue a TEST UNIT READY command to the device.

                        emc_clariion
                                    (Hardware-dependent) Query the  DGC/EMC  specific  EVPD  page
                                    0xC0  to  determine the path state for CLARiiON CX/AX and EMC
                                    VNX and Unity arrays families.

                        hp_sw       (Hardware-dependent) Check the path state  for  HP/COMPAQ/DEC
                                    HSG80   and   MSA/HSV   arrays   with   Active/Standby   mode
                                    exclusively.

                        rdac        (Hardware-dependent)    Check    the    path    state     for
                                    LSI/Engenio/NetApp  RDAC  class  as  NetApp  SANtricity  E/EF
                                    Series, and OEM arrays from IBM DELL SGI STK and SUN.

                        directio    Read the first sector with direct  I/O.  This  checker  could
                                    cause  spurious  path  failures  under  high load. Increasing
                                    checker_timeout can help with this.

                        cciss_tur   (Hardware-dependent) Check the path state for HP/COMPAQ Smart
                                    Array(CCISS) controllers.

                        none        Do not check the device, fallback to use the values retrieved
                                    from sysfs

                        The default is: tur

       alias_prefix     The user_friendly_names prefix.

                        The default is: mpath

       failback         Tell multipathd how to manage path group failback.  To  select  immediate
                        or  a  value,  it's  mandatory  that the device has support for a working
                        prioritizer.

                        immediate   Immediately failback to the highest priority  pathgroup  that
                                    contains active paths.

                        manual      Do not perform automatic failback.

                        followover  Used  to  deal  with  multiple  computers  accessing the same
                                    Active/Passive  storage  devices.  Only   perform   automatic
                                    failback  when  the first path of a pathgroup becomes active.
                                    This keeps a cluster node  from  automatically  failing  back
                                    when another node requested the failover.

                        values > 0  Deferred failback (time to defer in seconds).

                        The default is: manual

       rr_min_io        Number of I/O requests to route to a path before switching to the next in
                        the same path group. This is only for Block I/O(BIO) based multipath  and
                        only apply to round-robin path_selector.

                        The default is: 1000

       rr_min_io_rq     Number of I/O requests to route to a path before switching to the next in
                        the same path group. This is only for Request based  multipath  and  only
                        apply to round-robin path_selector.

                        The default is: 1

       max_fds          Specify  the  maximum  number  of  file descriptors that can be opened by
                        multipath and multipathd. This is equivalent to ulimit -n. A value of max
                        will  set  this to the system limit from /proc/sys/fs/nr_open. If this is
                        not set, the maximum number  of  open  fds  is  taken  from  the  calling
                        process.  It  is  usually  1024.  To  be  safe, this should be set to the
                        maximum number of paths plus 32, if that number is greated than 1024.

                        The default is: max

       rr_weight        If set to priorities the multipath configurator will assign path  weights
                        as  "path  prio * rr_min_io". Possible values are priorities or uniform .
                        Only apply to round-robin path_selector.

                        The default is: uniform

       no_path_retry    Specify what to do when all paths are down. Possible values are:

                        value > 0   Number of retries until disable I/O queueing.

                        fail        For immediate failure (no I/O queueing).

                        queue       For never stop I/O queueing, similar to queue_if_no_path. See
                                    KNOWN ISSUES.

                        The default is: fail

       queue_without_daemon
                        If set to no , when multipathd stops, queueing will be turned off for all
                        devices.  This is useful for devices that set no_path_retry. If a machine
                        is shut down while all paths to a device are down, it is possible to hang
                        waiting for I/O to return from  the  device  after  multipathd  has  been
                        stopped.  Without  multipathd  running,  access  to  the  paths cannot be
                        restored, and the kernel cannot be told to  stop  queueing  I/O.  Setting
                        queue_without_daemon to no , avoids this problem.

                        The default is: no

       checker_timeout  Specify  the  timeout  to  use  for  path  checkers  and prioritizers, in
                        seconds.  Only prioritizers that issue scsi commands use checker_timeout.
                        If  a  path does not respond to the checker command after checker_timeout
                        seconds have elapsed, it is considered down.

                        The default is: in /sys/block/<dev>/device/timeout

       allow_usb_devices
                        If set to no , all USB devices will be skipped during path discovery.  If
                        you intend to use multipath on USB attached devices, set this to yes.

                        The default is: no

       flush_on_last_del
                        If  set to yes , multipathd will disable queueing when the last path to a
                        device has been deleted.

                        The default is: no

       user_friendly_names
                        If set to yes , using the bindings file /etc/multipath/bindings to assign
                        a  persistent and unique alias to the multipath, in the form of mpath<n>.
                        If set to no use the WWID as the alias. In either case this  be  will  be
                        overridden by any specific aliases in the multipaths section.

                        The default is: no

       fast_io_fail_tmo Specify  the  number  of seconds the SCSI layer will wait after a problem
                        has been detected on a FC remote port before failing I/O  to  devices  on
                        that remote port.  This should be smaller than dev_loss_tmo. Setting this
                        to off will disable the timeout.

                        The default is: 5

       dev_loss_tmo     Specify the number of seconds the SCSI layer will wait  after  a  problem
                        has been detected on a FC remote port before removing it from the system.
                        This can be set  to  "infinity"  which  sets  it  to  the  max  value  of
                        2147483647 seconds, or 68 years. It will be automatically adjusted to the
                        overall retry interval no_path_retry * polling_interval if  a  number  of
                        retries  is  given  with  no_path_retry and the overall retry interval is
                        longer than the specified dev_loss_tmo value.  The Linux kernel will  cap
                        this value to 600 if fast_io_fail_tmo is not set. See KNOWN ISSUES.

                        The default is: 600

       eh_deadline      Specify  the  maximum  number  of seconds the SCSI layer will spend doing
                        error handling when scsi devices fail. After this timeout the scsi  layer
                        will  perform  a  full  HBA reset. Setting this may be necessary in cases
                        where the rport is never lost, so fast_io_fail_tmo and dev_loss_tmo  will
                        never  trigger,  but  (frequently  do  to load) scsi commands still hang.
                        Note: when the scsi error handler performs  the  HBA  reset,  all  target
                        paths  on  that  HBA  will be affected. eh_deadline should only be set in
                        cases where all targets on the affected HBAs are multipathed.

                        The default is: <unset>

       bindings_file    This option is deprecated, and will be removed in a future release.   The
                        full pathname of the binding file to be used when the user_friendly_names
                        option is set.

                        The default is: /etc/multipath/bindings

       wwids_file       This option is deprecated, and will be removed in a future release.   The
                        full pathname of the WWIDs file, which is used by multipath to keep track
                        of the WWIDs for LUNs it has created multipath devices on in the past.

                        The default is: /etc/multipath/wwids

       prkeys_file      This option is deprecated, and will be removed in a future release.   The
                        full  pathname  of  the  prkeys file, which is used by multipathd to keep
                        track of the persistent reservation key used for a  specific  WWID,  when
                        reservation_key is set to file.

                        The default is: /etc/multipath/prkeys

       log_checker_err  If  set to once , multipathd logs the first path checker error at logging
                        level 2. Any later errors are logged at  level  3  until  the  device  is
                        restored.  If  set  to  always  , multipathd always logs the path checker
                        error at logging level 2.

                        The default is: always

       reservation_key  This is the service action reservation key used by mpathpersist. It  must
                        be  set  for  all multipath devices using persistent reservations, and it
                        must be the same as the RESERVATION KEY field of the  PERSISTENT  RESERVE
                        OUT  parameter  list  which  contains  an  8-byte  value  provided by the
                        application client to the device server to identify the I_T nexus. If the
                        --param-aptpl  option is used when registering the key with mpathpersist,
                        :aptpl must be appended to the end of the reservation key.

                        Alternatively, this can be set to file, which will store the  RESERVATION
                        KEY  registered  by mpathpersist in the prkeys_file. multipathd will then
                        use this key to register additional  paths  as  they  appear.   When  the
                        registration  is  removed,  the  RESERVATION  KEY  is  removed  from  the
                        prkeys_file. The prkeys file will automatically keep track of whether the
                        key was registered with --param-aptpl.

                        The default is: <unset>

       all_tg_pt        Set the 'all targets ports' flag when registering keys with mpathpersist.
                        Some arrays automatically set and clear registration keys on  all  target
                        ports  from  a  host,  instead of per target port per host. The ALL_TG_PT
                        flag must be set  to  successfully  use  mpathpersist  on  these  arrays.
                        Setting  this  option  is identical to calling mpathpersist with --param-
                        alltgpt

                        The default is: no

       retain_attached_hw_handler
                        (Obsolete for kernels >= 4.3) If set  to  yes  and  the  SCSI  layer  has
                        already  attached  a  hardware_handler  to the device, multipath will not
                        force the device to use the hardware_handler specified by  mutipath.conf.
                        If  the  SCSI  layer  has not attached a hardware handler, multipath will
                        continue to use its configured hardware handler.

                        The default is: yes

                        Important  Note:  Linux  kernel  4.3  or  newer  always  behaves  as   if
                        "retain_attached_hw_handler yes" was set.

       detect_prio      If  set  to  yes  ,  multipath  will try to detect if the device supports
                        SCSI-3  ALUA.  If  so,  the  device  will  automatically  use  the  sysfs
                        prioritizer   if   the   required   sysf   attributes   access_state  and
                        preferred_path are supported, or the alua prioritizer if not. If  set  to
                        no , the prioritizer will be selected as usual.

                        The default is: yes

       detect_checker   if  set  to  yes  ,  multipath  will try to detect if the device supports
                        SCSI-3 ALUA. If so, the device will automatically use the tur checker. If
                        set to no , the checker will be selected as usual.

                        The default is: yes

       force_sync       If set to yes , multipathd will call the path checkers in sync mode only.
                        This means that only one checker will run at a time.  This is  useful  in
                        the  case  where  many  multipathd  checkers  running  in parallel causes
                        significant CPU pressure.

                        The default is: no

       strict_timing    If set to yes , multipathd will start  a  new  path  checker  loop  after
                        exactly  one  second,  so  that  each  path  check  will occur at exactly
                        polling_interval seconds. On busy systems path checks might  take  longer
                        than one second; here the missing ticks will be accounted for on the next
                        round.  A warning will  be  printed  if  path  checks  take  longer  than
                        polling_interval seconds.

                        The default is: no

       deferred_remove  If set to yes , multipathd will do a deferred remove instead of a regular
                        remove when the last path device has been deleted.  This  means  that  if
                        the multipath device is still in use, it will be freed when the last user
                        closes it.  If path is added to the multipath device before the last user
                        closes it, the deferred remove will be canceled.

                        The default is: no

       partition_delimiter
                        This  parameter  controls  how  multipath  chooses the names of partition
                        devices of multipath maps if a multipath map is renamed (e.g.  if  a  map
                        alias  is  added  or changed). If this parameter is set to a string other
                        than "/UNSET/" (even the empty string),  multipath  inserts  that  string
                        between  device  name  and  partition  number  to construct the partition
                        device name.  Otherwise (i.e. if this parameter is unset or has the value
                        "/UNSET/"),  the behavior depends on the map name: if it ends in a digit,
                        a "p" is inserted between  name  and  partition  number;  otherwise,  the
                        partition  number  is  simply appended.  Distributions may use a non-null
                        default value for this option; in this case, the  user  must  set  it  to
                        "/UNSET/"  to  obtain  the original <unset> behavior. Use multipath -T to
                        check the current settings.

                        The default is: <unset>

       config_dir       This option is deprecated, and will be removed in a future  release.   If
                        set  to  anything  other  than  "",  multipath will search this directory
                        alphabetically for file ending in ".conf" and it will read  configuration
                        information  from  them,  just  as  if  it  was  in  /etc/multipath.conf.
                        config_dir must either be "" or a fully qualified directory name.

                        The default is: /etc/multipath/conf.d/

       san_path_err_threshold
                        If set to a value greater than 0, multipathd will watch paths  and  check
                        how  many  times  a  path  has been failed due to errors.If the number of
                        failures on a particular path is greater then the san_path_err_threshold,
                        then  the  path will not reinstate till san_path_err_recovery_time. These
                        path failures should occur within a san_path_err_forget_rate  checks,  if
                        not  we will consider the path is good enough to reinstantate. See "Shaky
                        paths detection" below.

                        The default is: no

       san_path_err_forget_rate
                        If set to a value greater than 0, multipathd will check whether the  path
                        failures has exceeded  the san_path_err_threshold within this many checks
                        i.e san_path_err_forget_rate . If so we will not reinstante the path till
                        san_path_err_recovery_time. See "Shaky paths detection" below.

                        The default is: no

       san_path_err_recovery_time
                        If  set  to  a  value greater than 0, multipathd will make sure that when
                        path   failures   has   exceeded   the   san_path_err_threshold    within
                        san_path_err_forget_rate then the path will be placed in failed state for
                        san_path_err_recovery_time duration.Once  san_path_err_recovery_time  has
                        timeout  we will reinstante the failed path .  san_path_err_recovery_time
                        value should be in secs.  See "Shaky paths detection" below.

                        The default is: no

       marginal_path_double_failed_time
                        One of the four parameters of supporting path check based  on  accounting
                        IO  error  such  as  intermittent  error. When a path failed event occurs
                        twice in marginal_path_double_failed_time seconds due to an IO error  and
                        all the other three parameters are set, multipathd will fail the path and
                        enqueue this path into a queue of which members  are  sent  a  couple  of
                        continuous direct reading asynchronous IOs at a fixed sample rate of 10HZ
                        to start IO error accounting process. See "Shaky paths detection" below.

                        The default is: no

       marginal_path_err_sample_time
                        One of the four parameters of supporting path check based  on  accounting
                        IO error such as intermittent error. If it is set to a value no less than
                        120,    when    a     path     fail     event     occurs     twice     in
                        marginal_path_double_failed_time  second  due  to an IO error, multipathd
                        will fail the path and enqueue this path into a queue  of  which  members
                        are  sent  a  couple  of  continuous direct reading asynchronous IOs at a
                        fixed sample rate of 10HZ to start the IO accounting process for the path
                        will  last for marginal_path_err_sample_time.  If the rate of IO error on
                        a particular path is greater than  the  marginal_path_err_rate_threshold,
                        then  the  path will not reinstate for marginal_path_err_recheck_gap_time
                        seconds   unless   there    is    only    one    active    path.    After
                        marginal_path_err_recheck_gap_time  expires,  the  path will be requeueed
                        for rechecking. If checking result is  good  enough,  the  path  will  be
                        reinstated. See "Shaky paths detection" below.

                        The default is: no

       marginal_path_err_rate_threshold
                        The  error  rate  threshold  as  a  permillage  (1/1000). One of the four
                        parameters of supporting path check based on accounting IO error such  as
                        intermittent  error.  Refer to marginal_path_err_sample_time. If the rate
                        of IO errors on a particular path is greater than  this  parameter,  then
                        the   path  will  not  reinstate  for  marginal_path_err_recheck_gap_time
                        seconds unless there is only one active path. See "Shaky paths detection"
                        below.

                        The default is: no

       marginal_path_err_recheck_gap_time
                        One  of  the four parameters of supporting path check based on accounting
                        IO     error     such     as     intermittent     error.     Refer     to
                        marginal_path_err_sample_time.  If  this  parameter  is set to a positive
                        value, the failed path of   which  the  IO  error  rate  is  larger  than
                        marginal_path_err_rate_threshold   will  be  kept  in  failed  state  for
                        marginal_path_err_recheck_gap_time             seconds.              When
                        marginal_path_err_recheck_gap_time  seconds  expires,  the  path  will be
                        requeueed for checking. If checking result is good enough, the path  will
                        be  reinstated,  or else it will keep failed. See "Shaky paths detection"
                        below.

                        The default is: no

       delay_watch_checks
                        This option is deprecated, and mapped  to  san_path_err_forget_rate.   If
                        this  is  set  to  a value greater than 0 and no san_path_err options are
                        set,   san_path_err_forget_rate   will   be   set   to   the   value   of
                        delay_watch_checks  and san_path_err_threshold will be set to 1.  See the
                        san_path_err_forget_rate and san_path_err_threshold options,  and  "Shaky
                        paths detection" below for more information.

                        The default is: no

       delay_wait_checks
                        This  option is deprecated, and mapped to san_path_err_recovery_time.  If
                        this is set to a value greater than 0 and  no  san_path_err  options  are
                        set,   san_path_err_recovery_time   will   be   set   to   the  value  of
                        delay_wait_checks   times   max_polling_interval.    This    will    give
                        approximately  the  same  wait  time as delay_wait_checks previously did.
                        Also,   san_path_err_threshold   will   be   set   to    1.    See    the
                        san_path_err_recovery_time and san_path_err_threshold options, and "Shaky
                        paths detection" below for more information.

                        The default is: no

       marginal_pathgroups
                        If set to no, the  delay_*_checks,  marginal_path_*,  and  san_path_err_*
                        options will keep marginal, or "shaky", paths from being reinstated until
                        they have been monitored for some time. This can cause  situations  where
                        all non-marginal paths are down, and no paths are usable until multipathd
                        detects this and reinstates a marginal path. If the multipath  device  is
                        not configured to queue IO in this case, it can cause IO errors to occur,
                        even though there are marginal paths available.  However, if this  option
                        is set to yes, when one of the marginal path detecting methods determines
                        that a path is marginal, it will be reinstated and placed in  a  seperate
                        pathgroup  that  will  only be used after all the non-marginal pathgroups
                        have been tried  first.  This  prevents  the  possibility  of  IO  errors
                        occuring  while  marginal paths are still usable. After the path has been
                        monitored for the configured time, and is declared healthy,  it  will  be
                        returned  to  its normal pathgroup. See "Shaky paths detection" below for
                        more information.

                        The default is: no

       find_multipaths  This option controls whether  multipath  and  multipathd  try  to  create
                        multipath  maps over non-blacklisted devices they encounter. This matters
                        a) when a  device  is  encountered  by  multipath  -u  during  udev  rule
                        processing  (a device is blocked from further processing by higher layers
                        - such as LVM - if and only if it´s considered a valid  multipath  device
                        path),  and b) when multipathd detects a new device. The following values
                        are possible:

                        strict    Both multipath  and  multipathd  treat  only  such  devices  as
                                  multipath  devices  which  have  been  part  of a multipath map
                                  previously, and which are therefore listed in  the  wwids_file.
                                  Users  can  manually set up multipath maps using the multipathd
                                  add map command. Once set up manually, the map is remembered in
                                  the wwids file and will be set up automatically in the future.

                        no        Multipath behaves like strict. Multipathd behaves like greedy.

                        yes       Both  multipathd  and  multipath  treat  a  device as multipath
                                  device if the conditions for strict are met, or if at least two
                                  non-blacklisted paths with the same WWID have been detected.

                        greedy    Both  multipathd  and  multipath  treat  every  non-blacklisted
                                  device as multipath device path.

                        smart     This differs from find_multipaths yes only in the way it treats
                                  new devices for which only one path has been detected yet. When
                                  such a device is first encounted in udev rules, it  is  treated
                                  as  a  multipath  device.  multipathd  waits whether additional
                                  paths with the same WWID appears. If that happens, it sets up a
                                  multipath map. If it doesn´t happen until a timeout expires, or
                                  if setting up the map fails, a new uevent is triggered for  the
                                  device;  at second encounter in the udev rules, the device will
                                  be treated as non-multipath and  passed  on  to  upper  layers.
                                  Note:  this  may  cause delays during device detection if there
                                  are single-path devices which aren´t blacklisted.

                        The default is: strict

       find_multipaths_timeout
                        Timeout, in seconds, to wait for additional  paths  after  detecting  the
                        first one, if find_multipaths "smart" (see above) is set. If the value is
                        positive, this timeout is used for all unknown,  non-blacklisted  devices
                        encountered. If the value is negative (recommended), it's only applied to
                        "known" devices that have an entry in multipath's hardware table,  either
                        in  the  built-in table or in a device section; other ("unknown") devices
                        will use a timeout of only 1 second to avoid booting delays. The value  0
                        means  "use  the  built-in  default". If find_multipath has a value other
                        than smart, this option has no effect.

                        The default is: -10 (10s for known and 1s for unknown hardware)

       uxsock_timeout   CLI receive timeout in milliseconds.  For  larger  systems  CLI  commands
                        might  timeout before the multipathd lock is released and the CLI command
                        can be processed. This will result  in  errors  like  "timeout  receiving
                        packet"  to  be  returned  from  CLI  commands.   In  these  cases  it is
                        recommended to increase the CLI timeout to avoid those issues.

                        The default is: 4000

       retrigger_tries  Sets the number of times multipathd will try to retrigger a uevent to get
                        the WWID.

                        The default is: 3

       retrigger_delay  Sets the amount of time, in seconds, to wait between retriggers.

                        The default is: 10

       missing_uev_wait_timeout
                        Controls  how  many  seconds  multipathd will wait, after a new multipath
                        device is created, to receive a change event from udev  for  the  device,
                        before  automatically  enabling  device  reloads. Usually multipathd will
                        delay reloads on a device until it receives  a  change  uevent  from  the
                        initial table load.

                        The default is: 30

       skip_kpartx      If  set  to  yes , kpartx will not automatically create partitions on the
                        device.

                        The default is: no

       disable_changed_wwids
                        This option is deprecated and ignored. If the WWID  of  a  path  suddenly
                        changes, multipathd handles it as if it was removed and then added again.

       remove_retries   This  sets  how  may times multipath will retry removing a device that is
                        in-use.  Between each attempt, multipath will sleep 1 second.

                        The default is: 0

       max_sectors_kb   Sets the max_sectors_kb device parameter on  all  path  devices  and  the
                        multipath device to the specified value.

                        The default is: in /sys/block/<dev>/queue/max_sectors_kb

       ghost_delay      Sets  the  number  of  seconds  that multipath will wait after creating a
                        device with only ghost paths before marking it ready for use in  systemd.
                        This  gives the active paths time to appear before the multipath runs the
                        hardware handler to switch the ghost paths to active ones.  Setting  this
                        to  0  or  no  makes  multipath immediately mark a device with only ghost
                        paths as ready.

                        The default is: no

       enable_foreign   Enables or disables foreign  libraries  (see  section  FOREIGN  MULTIPATH
                        SUPPORT  below). The value is a regular expression; foreign libraries are
                        loaded if their name (e.g. "nvme") matches the expression. By default, no
                        foreign  libraries  are enabled. Set this to "nvme" to enable NVMe native
                        multipath support, or ".*" to enable all foreign libraries.

                        The default is: "NONE"

       recheck_wwid     If set to yes, when a failed path is restored, its wwid is rechecked.  If
                        the  wwid  has  changed,  the  path is removed from the current multipath
                        device, and re-added as a new path. Multipathd will also recheck a path's
                        wwid  if it is manually re-added. This option only works for SCSI devices
                        that are configured to use the default uid_attribute, ID_SERIAL, or sysfs
                        for getting their wwid.

                        The default is: no

blacklist and blacklist_exceptions sections

       The  blacklist section is used to exclude specific devices from the multipath topology. It
       is most commonly used to exclude local disks or non-disk devices (such  as  LUNs  for  the
       storage array controller) from being handled by multipath-tools.

       In  the  blacklist  and  blacklist_exceptions  sections,  starting  a quoted value with an
       exclamation mark "!" will invert the matching of the rest of the regular  expression.  For
       instance,  "!^sd[a-z]"  will  match  all  values  that  do  not  start with "sd[a-z]". The
       exclamation mark can be escaped "\!" to match a literal  !  at  the  start  of  a  regular
       expression. Note: The exclamation mark must be inside quotes, otherwise it will be treated
       as starting a comment.

       The blacklist_exceptions section is used to revert the actions of the  blacklist  section.
       This  allows  one  to  selectively  include  ("whitelist") devices which would normally be
       excluded via the blacklist section. A common usage is to blacklist  "everything"  using  a
       catch-all  regular  expression, and create specific blacklist_exceptions entries for those
       devices that should be handled by multipath-tools.

       The following keywords are recognized in both sections.  The  defaults  are  empty  unless
       explicitly stated.

       devnode          Regular expression matching the device nodes to be excluded/included.

                        The  default  blacklist  consists  of  the  regular  expression "!^(sd[a-
                        z]|dasd[a-z]|nvme[0-9])". This causes all device types other  than  scsi,
                        dasd, and nvme to be excluded from multipath handling by default.

       wwid             Regular  expression  for  the  World  Wide  Identifier  of a device to be
                        excluded/included.

       device           Subsection for the device description.  This  subsection  recognizes  the
                        vendor  and  product  keywords.  Both are regular expressions. For a full
                        description of these keywords please see the devices section description.

       property         Regular expression for an udev property. All devices that  have  matching
                        udev  properties will be excluded/included.  The handling of the property
                        keyword is special, because devices must have at  least  one  whitelisted
                        udev  property; otherwise they're treated as blacklisted, and the message
                        "blacklisted, udev property missing" is displayed in the logs.

                        Note: The behavior of this option has changed  in  multipath-tools  0.8.2
                        compared  to  previous  versions.   Blacklisting by missing properties is
                        only  applied  to  devices  which  do  have  the  property  specified  by
                        uid_attribute  (e.g.  ID_SERIAL) set. Previously, it was applied to every
                        device, possibly causing devices to be blacklisted because  of  temporary
                        I/O error conditions.

                        The  default  blacklist exception is: (SCSI_IDENT_|ID_WWN), causing well-
                        behaved SCSI devices and devices that provide a WWN (World  Wide  Number)
                        to be included, and all others to be excluded.

       protocol         Regular expression for the protocol of a device to be excluded/included.

                        The  protocol  strings  that multipath recognizes are scsi:fcp, scsi:spi,
                        scsi:ssa, scsi:sbp, scsi:srp, scsi:iscsi, scsi:sas,  scsi:adt,  scsi:ata,
                        scsi:unspec,  ccw,  cciss,  nvme, and undef.  The protocol that a path is
                        using can be viewed by running multipathd show paths format "%d %P"

       For every device, these 5 blacklist criteria are evaluated in  the  the  order  "property,
       devnode,  device,  protocol,  wwid".  If  a  device  turns  out  to  be blacklisted by any
       criterion, it's excluded from handling  by  multipathd,  and  the  later  criteria  aren't
       evaluated  any more. For each criterion, the whitelist takes precedence over the blacklist
       if a device matches both.

       Note:  Besides  the  blacklist  and  whitelist,  other  configuration  options   such   as
       find_multipaths  have  an impact on whether or not a given device is handled by multipath-
       tools.

multipaths section

       The multipaths section allows setting attributes of multipath maps.  The  attributes  that
       are  set  via  the  multipaths  section  (see  list  below) take precedence over all other
       configuration settings, including those from the overrides section.

       The only recognized attribute for the multipaths section is the multipath  subsection.  If
       there  are  multiple  multipath  subsections  matching a given WWID, the contents of these
       sections are merged, and settings from later entries take precedence.

       The multipath subsection recognizes the following attributes:

       wwid             (Mandatory) World Wide Identifier. Detected multipath  maps  are  matched
                        agains  this  attribute.   Note  that,  unlike  the wwid attribute in the
                        blacklist section, this is not a regular expression or a substring; WWIDs
                        must match exactly inside the multipaths section.

       alias            Symbolic  name  for  the  multipath  map. This takes precedence over a an
                        entry for the same WWID in the bindings_file.

       The following attributes are optional; if not set the default values are  taken  from  the
       overrides, devices, or defaults section:

              path_grouping_policy
              path_selector
              prio
              prio_args
              failback
              rr_weight
              no_path_retry
              rr_min_io
              rr_min_io_rq
              flush_on_last_del
              features
              reservation_key
              user_friendly_names
              deferred_remove
              san_path_err_threshold
              san_path_err_forget_rate
              san_path_err_recovery_time
              marginal_path_err_sample_time
              marginal_path_err_rate_threshold
              marginal_path_err_recheck_gap_time
              marginal_path_double_failed_time
              delay_watch_checks
              delay_wait_checks
              skip_kpartx
              max_sectors_kb
              ghost_delay

devices section

       multipath-tools  have  a  built-in device table with reasonable defaults for more than 100
       known multipath-capable storage devices. The devices section can be used to override these
       settings. If there are multiple matches for a given device, the attributes of all matching
       entries are applied to it.  If an  attribute  is  specified  in  several  matching  device
       subsections,  later  entries  take precedence. Thus, entries in files under config_dir (in
       reverse  alphabetical  order)  have  the  highest  precedence,  followed  by  entries   in
       multipath.conf;   the  built-in  hardware  table  has  the  lowest  precedence.  Inside  a
       configuration file, later entries have higher precedence than earlier ones.

       The only recognized attribute for the devices section is the  device  subsection.  Devices
       detected  in  the system are matched against the device entries using the vendor, product,
       and revision fields, which are all POSIX Extended regular expressions (see regex(7)).

       The vendor, product, and revision fields that multipath or multipathd detect  for  devices
       in a system depend on the device type. For SCSI devices, they correspond to the respective
       fields of the SCSI INQUIRY page. In general, the command 'multipathd show paths format "%d
       %s"' command can be used to see the detected properties for all devices in the system.

       The device subsection recognizes the following attributes:

       vendor           (Mandatory) Regular expression to match the vendor name.

       product          (Mandatory) Regular expression to match the product name.

       revision         Regular  expression  to match the product revision. If not specified, any
                        revision matches.

       product_blacklist
                        Products with the given vendor matching this string are blacklisted. This
                        is  equivalent to a device entry in the blacklist section with the vendor
                        attribute set to this entry's vendor, and the product  attribute  set  to
                        the value of product_blacklist.

       alias_prefix     The  user_friendly_names  prefix  to use for this device type, instead of
                        the default "mpath".

       vpd_vendor       The  vendor  specific  vpd  page  information,   using   the   vpd   page
                        abbreviation.   The  vpd page abbreviation can be found by running sg_vpd
                        -e. multipathd will  use  this  information  to  gather  device  specific
                        information  that can be displayed with the %g wilcard for the multipathd
                        show maps format and multipathd show  paths  format  commands.  Currently
                        only the hp3par vpd page is supported.

       hardware_handler The hardware handler to use for this device type.  The following hardware
                        handler are implemented:

                        1 emc       (Hardware-dependent) Hardware handler for DGC class arrays as
                                    CLARiiON CX/AX and EMC VNX and Unity families.

                        1 rdac      (Hardware-dependent)  Hardware handler for LSI/Engenio/NetApp
                                    RDAC class as NetApp SANtricity E/EF Series, and  OEM  arrays
                                    from IBM DELL SGI STK and SUN.

                        1 hp_sw     (Hardware-dependent) Hardware handler for HP/COMPAQ/DEC HSG80
                                    and MSA/HSV arrays with Active/Standby mode exclusively.

                        1 alua      (Hardware-dependent)  Hardware  handler   for   SCSI-3   ALUA
                                    compatible arrays.

                        1 ana       (Hardware-dependent) Hardware handler for NVMe ANA compatible
                                    arrays.

                        The default is: <unset>

                        Important Note: Linux kernels 4.3 and newer automatically attach a device
                        handler  to  known  devices (which includes all devices supporting SCSI-3
                        ALUA)   and   disallow   changing   the   handler   afterwards.   Setting
                        hardware_handler for such devices on these kernels has no effect.

       The  following  attributes  are optional; if not set the default values are taken from the
       defaults section:

              path_grouping_policy
              uid_attribute
              getuid_callout
              path_selector
              path_checker
              prio
              prio_args
              features
              failback
              rr_weight
              no_path_retry
              rr_min_io
              rr_min_io_rq
              fast_io_fail_tmo
              dev_loss_tmo
              flush_on_last_del
              user_friendly_names
              retain_attached_hw_handler
              detect_prio
              detect_checker
              deferred_remove
              san_path_err_threshold
              san_path_err_forget_rate
              san_path_err_recovery_time
              marginal_path_err_sample_time
              marginal_path_err_rate_threshold
              marginal_path_err_recheck_gap_time
              marginal_path_double_failed_time
              delay_watch_checks
              delay_wait_checks
              skip_kpartx
              max_sectors_kb
              ghost_delay
              all_tg_pt

overrides section

       The overrides section recognizes the following optional attributes; if not set the  values
       are taken from the devices or defaults sections:

              path_grouping_policy
              uid_attribute
              getuid_callout
              path_selector
              path_checker
              alias_prefix
              features
              prio
              prio_args
              failback
              rr_weight
              no_path_retry
              rr_min_io
              rr_min_io_rq
              flush_on_last_del
              fast_io_fail_tmo
              dev_loss_tmo
              user_friendly_names
              retain_attached_hw_handler
              detect_prio
              detect_checker
              deferred_remove
              san_path_err_threshold
              san_path_err_forget_rate
              san_path_err_recovery_time
              marginal_path_err_sample_time
              marginal_path_err_rate_threshold
              marginal_path_err_recheck_gap_time
              marginal_path_double_failed_time
              delay_watch_checks
              delay_wait_checks
              skip_kpartx
              max_sectors_kb
              ghost_delay
              all_tg_pt

WWID generation

       Multipath  uses  a World Wide Identification (WWID) to determine which paths belong to the
       same device. Each path presenting the same WWID is assumed to point to the same device.

       The WWID is generated by four methods (in the order of preference):

       uid_attrs        The WWID is derived from udev attributes  by  matching  the  device  node
                        name; cf uid_attrs above.

       getuid_callout   Use the specified external program; cf getuid_callout above.  Care should
                        be taken when using this method; the external program needs to be  loaded
                        from  disk  for  execution, which might lead to deadlock situations in an
                        all-paths-down scenario.

       uid_attribute    Use the value of the specified udev attribute;  cf  uid_attribute  above.
                        This  method is preferred to getuid_callout as multipath does not need to
                        call any external programs here.  However,  under  certain  circumstances
                        udev might not be able to generate the requested variable.

       sysfs            Try  to determine the WWID from sysfs attributes.  For SCSI devices, this
                        means reading the Vital Product Data (VPD) page  "Device  Identification"
                        (0x83).

       The  default  settings (using udev and uid_attribute configured from the built-in hardware
       table) should work fine in most scenarios. Users who want to enable  uevent  merging  must
       set uid_attrs.

Shaky paths detection

       A  common  problem  in  SAN  setups  is  the  occurence  of intermittent errors: a path is
       unreachable, then reachable again for a short time, disappears again, and so  forth.  This
       happens  typically  on  unstable  interconnects.  It  is  undesirable to switch pathgroups
       unnecessarily on such frequent, unreliable events.  multipathd  supports  three  different
       methods for detecting this situation and dealing with it. All methods share the same basic
       mode of operation: If a path is found to be "shaky" or "flipping", and appears  to  be  in
       healthy  status, it is not reinstated (put back to use) immediately. Instead, it is placed
       in the "delayed" state and watched for some time, and only reinstated if the healthy state
       appears  to be stable.  If the marginal_pathgroups option is set, the path will reinstated
       immediately, but placed in a special pathgroup for  marginal  paths.  Marginal  pathgroups
       will  not  be  used  until all other pathgroups have been tried. At the time when the path
       would normally be reinstated, it will be returned to its normal pathgroup.  The  logic  of
       determining "shaky" condition, as well as the logic when to reinstate, differs between the
       three methods.

       "delay_checks" failure tracking
               This method is deprecated and  mapped  to  the  "san_path_err"  method.   See  the
               delay_watch_checks and delay_wait_checks options above for more information.

       "marginal_path" failure tracking
               If    a    second    failure    event   (good->bad   transition)   occurs   within
               marginal_path_double_failed_time   seconds   after   a   failure,   high-frequency
               monitoring  is  started  for  the  affected  path: I/O is sent at a rate of 10 per
               second. This  is  done  for  marginal_path_err_sample_time  seconds.  During  this
               period,  the  path  is  not  reinstated.  If  the  rate  of  errors  remains below
               marginal_path_err_rate_threshold  during  the  monitoring  period,  the  path   is
               reinstated.     Otherwise,     it     is     kept     in    failed    state    for
               marginal_path_err_recheck_gap_time, and after that, it  is  monitored  again.  For
               this method, time intervals are measured in seconds.

       "san_path_err" failure tracking
               multipathd counts path failures for each path. Once the number of failures exceeds
               the value  given  by  san_path_err_threshold,  the  path  is  not  reinstated  for
               san_path_err_recovery_time  seconds. While counting failures, multipathd "forgets"
               one past failure every "san_path_err_forget_rate"  ticks;  thus  if  errors  don't
               occur  more often then once in the forget rate interval, the failure count doesn't
               increase and the threshold is never reached.  Ticks  are  the  time  between  path
               checks by multipathd, which is variable and controlled by the polling_interval and
               max_polling_interval parameters.

               This method is deprecated in favor of the "marginal_path" failure tracking method,
               and only offered for backward compatibility.

       See  the  documentation  of  the  individual  options  above  for details.  It is strongly
       discouraged to use more than one of these methods for any given multipath map, because the
       two  concurrent  methods may interact in unpredictable ways. If the "marginal_path" method
       is active, the "san_path_err" parameters are implicitly set to 0.

FOREIGN MULTIPATH SUPPORT

       multipath  and  multipathd  can  load  "foreign"  libraries  to  add  support  for   other
       multipathing  technologies  besides  the  Linux  device mapper.  Currently this support is
       limited to printing detected information about multipath setup. In  topology  output,  the
       names  of  foreign maps are prefixed by the foreign library name in square brackets, as in
       this example:

       # multipath -ll
       uuid.fedcba98-3579-4567-8765-123456789abc [nvme]:nvme4n9 NVMe,Some NVMe controller,FFFFFFFF
       size=167772160 features='n/a' hwhandler='ANA' wp=rw
       |-+- policy='n/a' prio=50 status=optimized
       | `- 4:38:1    nvme4c38n1 0:0     n/a   optimized    live
       `-+- policy='n/a' prio=50 status=optimized
         `- 4:39:1    nvme4c39n1 0:0     n/a   optimized    live

       The "nvme" foreign library provides support for NVMe native multipathing in the kernel. It
       is part of the standard multipath package.

KNOWN ISSUES

       The  usage  of  queue_if_no_path  option  can lead to D state processes being hung and not
       killable in situations where all the paths to the LUN go offline. It is advisable  to  use
       the no_path_retry option instead.

       The  use of queue_if_no_path or no_path_retry might lead to a deadlock if the dev_loss_tmo
       setting results in a device being removed while I/O is still queued. The multipath  daemon
       will  update  the  dev_loss_tmo  setting accordingly to avoid this deadlock. Hence if both
       values  are  specified  the  order  of  precedence  is  no_path_retry,   queue_if_no_path,
       dev_loss_tmo.

SEE ALSO

       udev(8), dmsetup(8), multipath(8), multipathd(8).

AUTHORS

       multipath-tools  was developed by Christophe Varoqui, <christophe.varoqui@opensvc.com> and
       others.