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.