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NAME

       lvmraid — LVM RAID

DESCRIPTION

       lvm(8)  RAID  is a way to create a Logical Volume (LV) that uses multiple physical devices
       to improve performance or tolerate device failures.  In  LVM,  the  physical  devices  are
       Physical Volumes (PVs) in a single Volume Group (VG).

       How  LV  data blocks are placed onto PVs is determined by the RAID level.  RAID levels are
       commonly referred to as 'raid'  followed  by  a  number,  e.g.   raid1,  raid5  or  raid6.
       Selecting  a  RAID  level  involves  making tradeoffs among: physical device requirements,
       fault tolerance, and performance.  A description of the RAID levels can be found at
       www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf

       LVM RAID uses both Device Mapper (DM) and Multiple Device  (MD)  drivers  from  the  Linux
       kernel.  DM is used to create and manage visible LVM devices, and MD is used to place data
       on physical devices.

       LVM creates hidden LVs (dm devices) layered between the visible LV and  physical  devices.
       LVs  in  the  middle layers are called sub LVs.  For LVM raid, a sub LV pair to store data
       and metadata (raid superblock and write intent bitmap) is created per raid image/leg  (see
       lvs command examples below).

USAGE

       To  create  a  RAID LV, use lvcreate and specify an LV type.  The LV type corresponds to a
       RAID level.  The basic RAID levels that can be  used  are:  raid0,  raid1,  raid4,  raid5,
       raid6, raid10.

       lvcreate --type RaidLevel [OPTIONS] --name Name --size Size VG [PVs]

       To display the LV type of an existing LV, run:

       lvs -o name,segtype LV

       (The LV type is also referred to as "segment type" or "segtype".)

       LVs can be created with the following types:

   raid0
       Also  called  striping,  raid0  spreads LV data across multiple devices in units of stripe
       size.  This is used to increase performance.  LV data will be lost if any of  the  devices
       fail.

       lvcreate --type raid0 [--stripes Number --stripesize Size] VG [PVs]

       --stripes Number
              specifies the Number of devices to spread the LV across.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is the amount of data that is
              written to one device before moving to the next.

       PVs specifies the devices to use.  If not specified, lvm will choose Number  devices,  one
       for each stripe based on the number of PVs available or supplied.

   raid1
       Also  called  mirroring,  raid1  uses  multiple devices to duplicate LV data.  The LV data
       remains available if all but one of the devices fail.  The minimum number of devices (i.e.
       sub LV pairs) required is 2.

       lvcreate --type raid1 [--mirrors Number] VG [PVs]

       --mirrors Number
              specifies  the  Number  of mirror images in addition to the original LV image, e.g.
              --mirrors 1 means there are two images of the data, the  original  and  one  mirror
              image.

       PVs  specifies  the devices to use.  If not specified, lvm will choose Number devices, one
       for each image.

   raid4
       raid4 is a form of striping that uses an extra, first device dedicated to  storing  parity
       blocks.   The  LV  data  remains  available  if  one  device fails.  The parity is used to
       recalculate data that is lost from  a  single  device.   The  minimum  number  of  devices
       required is 3.

       lvcreate --type raid4 [--stripes Number --stripesize Size] VG [PVs]

       --stripes Number
              specifies  the  Number  of  devices  to use for LV data.  This does not include the
              extra device lvm adds for storing parity blocks.  A raid4 LV  with  Number  stripes
              requires Number+1 devices.  Number must be 2 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is the amount of data that is
              written to one device before moving to the next.

       PVs specifies the devices to use.  If not specified, lvm  will  choose  Number+1  separate
       devices.

       raid4  is  called  non-rotating  parity because the parity blocks are always stored on the
       same device.

   raid5
       raid5 is a form of striping that uses an extra device for storing parity blocks.  LV  data
       and  parity  blocks  are  stored  on  each  device,  typically  in  a rotating pattern for
       performance reasons.  The LV data remains available if one device fails.   The  parity  is
       used to recalculate data that is lost from a single device.  The minimum number of devices
       required is 3 (unless converting from 2 legged raid1  to  reshape  to  more  stripes;  see
       reshaping).

       lvcreate --type raid5 [--stripes Number --stripesize Size] VG [PVs]

       --stripes Number
              specifies  the  Number  of  devices  to use for LV data.  This does not include the
              extra device lvm adds for storing parity blocks.  A raid5 LV  with  Number  stripes
              requires Number+1 devices.  Number must be 2 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is the amount of data that is
              written to one device before moving to the next.

       PVs specifies the devices to use.  If not specified, lvm  will  choose  Number+1  separate
       devices.

       raid5  is called rotating parity because the parity blocks are placed on different devices
       in a round-robin sequence.  There are variations of raid5 with  different  algorithms  for
       placing  the  parity blocks.  The default variant is raid5_ls (raid5 left symmetric, which
       is a rotating parity 0 with data restart.)  See RAID5 VARIANTS below.

   raid6
       raid6 is a form of striping like raid5, but uses two extra devices for parity blocks.   LV
       data  and  parity  blocks  are  stored on each device, typically in a rotating pattern for
       performance reasons.  The LV data remains available if up to two devices fail.  The parity
       is  used  to recalculate data that is lost from one or two devices.  The minimum number of
       devices required is 5.

       lvcreate --type raid6 [--stripes Number --stripesize Size] VG [PVs]

       --stripes Number
              specifies the Number of devices to use for LV data.   This  does  not  include  the
              extra  two  devices  lvm  adds  for  storing parity blocks.  A raid6 LV with Number
              stripes requires Number+2 devices.  Number must be 3 or more.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is the amount of data that is
              written to one device before moving to the next.

       PVs  specifies  the  devices  to use.  If not specified, lvm will choose Number+2 separate
       devices.

       Like raid5, there are variations of raid6 with different algorithms for placing the parity
       blocks.  The default variant is raid6_zr (raid6 zero restart, aka left symmetric, which is
       a rotating parity 0 with data restart.)  See RAID6 VARIANTS below.

   raid10
       raid10 is a combination of raid1 and raid0, striping data  across  mirrored  devices.   LV
       data  remains  available  if  one or more devices remains in each mirror set.  The minimum
       number of devices required is 4.

       lvcreate --type raid10
              [--mirrors NumberMirrors]
              [--stripes NumberStripes --stripesize Size]
              VG [PVs]

       --mirrors NumberMirrors
              specifies the number of mirror images within each stripe.  e.g.  --mirrors 1  means
              there are two images of the data, the original and one mirror image.

       --stripes NumberStripes
              specifies the total number of devices to use in all raid1 images (not the number of
              raid1 devices to spread the LV across, even though that is the  effective  result).
              The number of devices in each raid1 mirror will be NumberStripes/(NumberMirrors+1),
              e.g. mirrors 1 and stripes 4 will stripe data across two raid1 mirrors, where  each
              mirror is devices.

       --stripesize Size
              specifies the Size of each stripe in kilobytes.  This is the amount of data that is
              written to one device before moving to the next.

       PVs specifies the devices to use.   If  not  specified,  lvm  will  choose  the  necessary
       devices.   Devices  are  used  to  create mirrors in the order listed, e.g. for mirrors 1,
       stripes 2, listing PV1 PV2 PV3 PV4 results in mirrors PV1/PV2 and PV3/PV4.

       RAID10 is not mirroring on top of stripes, which would be RAID01, which is  less  tolerant
       of device failures.

   Configuration Options
       There  are  a  number of options in the LVM configuration file that affect the behavior of
       RAID LVs.  The tunable options are listed below.  A detailed description of  each  can  be
       found in the LVM configuration file itself.
              mirror_segtype_default
              raid10_segtype_default
              raid_region_size
              raid_fault_policy
              activation_mode

   Monitoring
       When  a  RAID  LV is activated the dmeventd(8) process is started to monitor the health of
       the LV.  Various events detected in the kernel can cause a notification to  be  sent  from
       device-mapper  to  the  monitoring  process, including device failures and synchronization
       completion (e.g.  for initialization or scrubbing).

       The LVM configuration file contains options that affect how the  monitoring  process  will
       respond  to  failure  events  (e.g. raid_fault_policy).  It is possible to turn on and off
       monitoring with lvchange, but it is not recommended to turn this off  unless  you  have  a
       thorough knowledge of the consequences.

   Synchronization
       Synchronization  is  the  process  that makes all the devices in a RAID LV consistent with
       each other.

       In a RAID1 LV, all mirror images should have the same data.  When a new  mirror  image  is
       added,  or  a  mirror  image  is  missing data, then images need to be synchronized.  Data
       blocks are copied from an existing image to a new or outdated image to make them match.

       In a RAID 4/5/6 LV, parity blocks and  data  blocks  should  match  based  on  the  parity
       calculation.   When the devices in a RAID LV change, the data and parity blocks can become
       inconsistent and need to be synchronized.  Correct blocks are read, parity is  calculated,
       and recalculated blocks are written.

       The  RAID implementation keeps track of which parts of a RAID LV are synchronized.  When a
       RAID LV is first created and activated the first synchronization is called initialization.
       A  pointer  stored  in  the  raid  metadata keeps track of the initialization process thus
       allowing it to be restarted after a deactivation of the RaidLV or a crash.  Any writes  to
       the  RaidLV  dirties the respective region of the write intent bitmap which allow for fast
       recovery of the regions after a crash.  Without this, the  entire  LV  would  need  to  be
       synchronized every time it was activated.

       Automatic  synchronization  happens when a RAID LV is activated, but it is usually partial
       because the bitmaps reduce the areas that are checked.  A full sync becomes necessary when
       devices in the RAID LV are replaced.

       The  synchronization  status  of  a  RAID  LV  is reported by the following command, where
       "Cpy%Sync" = "100%" means sync is complete:

       lvs -a -o name,sync_percent

   Scrubbing
       Scrubbing is a full scan of the RAID LV requested by a user.  Scrubbing can find  problems
       that are missed by partial synchronization.

       Scrubbing  assumes  that  RAID  metadata and bitmaps may be inaccurate, so it verifies all
       RAID metadata, LV data, and parity blocks.  Scrubbing can find inconsistencies  caused  by
       hardware  errors  or  degradation.  These kinds of problems may be undetected by automatic
       synchronization which excludes areas outside of the RAID write-intent bitmap.

       The command to scrub a RAID LV can operate in two different modes:

       lvchange --syncaction check|repair LV

       check  Check mode is read-only and only detects inconsistent areas in the RAID LV, it does
              not correct them.

       repair Repair  mode  checks  and  writes  corrected blocks to synchronize any inconsistent
              areas.

       Scrubbing can consume a lot of bandwidth and slow down application I/O on the RAID LV.  To
       control the I/O rate used for scrubbing, use:

       --maxrecoveryrate Size[k|UNIT]
              Sets  the  maximum recovery rate for a RAID LV.  Size is specified as an amount per
              second for each device in the array.  If no suffix is given, then KiB/sec/device is
              used.  Setting the recovery rate to 0 means it will be unbounded.

       --minrecoveryrate Size[k|UNIT]
              Sets  the  minimum recovery rate for a RAID LV.  Size is specified as an amount per
              second for each device in the array.  If no suffix is given, then KiB/sec/device is
              used.  Setting the recovery rate to 0 means it will be unbounded.

       To  display  the current scrubbing in progress on an LV, including the syncaction mode and
       percent complete, run:

       lvs -a -o name,raid_sync_action,sync_percent

       After scrubbing is complete, to display the number of inconsistent blocks found, run:

       lvs -o name,raid_mismatch_count

       Also, if mismatches were found, the lvs attr field will display the letter "m"  (mismatch)
       in the 9th position, e.g.

       # lvs -o name,vgname,segtype,attr vg/lv
         LV VG   Type  Attr

         lv vg   raid1 Rwi-a-r-m-
   Scrubbing Limitations
       The  check  mode can only report the number of inconsistent blocks, it cannot report which
       blocks are inconsistent.  This makes it impossible to know which device has errors, or  if
       the errors affect file system data, metadata or nothing at all.

       The  repair  mode can make the RAID LV data consistent, but it does not know which data is
       correct.  The result may be consistent but incorrect data.  When two different  blocks  of
       data  must  be  made  consistent,  it chooses the block from the device that would be used
       during RAID initialization.  However, if the PV holding corrupt data  is  known,  lvchange
       --rebuild can be used in place of scrubbing to reconstruct the data on the bad device.

       Future developments might include:

       Allowing a user to choose the correct version of data during repair.

       Using  a  majority  of  devices to determine the correct version of data to use in a 3-way
       RAID1 or RAID6 LV.

       Using a checksumming device to pin-point when and where an error occurs, allowing it to be
       rewritten.

   SubLVs
       An  LV  is  often  a combination of other hidden LVs called SubLVs.  The SubLVs either use
       physical devices, or are built from other SubLVs themselves.  SubLVs hold LV data  blocks,
       RAID  parity blocks, and RAID metadata.  SubLVs are generally hidden, so the lvs -a option
       is required to display them:

       lvs -a -o name,segtype,devices

       SubLV names begin with the visible LV name, and have an automatic  suffix  indicating  its
       role:

            • SubLVs holding LV data or parity blocks have the suffix _rimage_#.
              These SubLVs are sometimes referred to as DataLVs.

            • SubLVs  holding  RAID  metadata  have  the suffix _rmeta_#.  RAID metadata includes
              superblock information, RAID type, bitmap, and device health information.
              These SubLVs are sometimes referred to as MetaLVs.

       SubLVs are an internal implementation detail of LVM.  The way they are  used,  constructed
       and named may change.

       The  following  examples  show  the SubLV arrangement for each of the basic RAID LV types,
       using the fewest number of devices allowed for each.

       Examples

       raid0
       Each rimage SubLV holds a portion of LV data.  No parity is used.   No  RAID  metadata  is
       used.

       # lvcreate --type raid0 --stripes 2 --name lvr0 ...

       # lvs -a -o name,segtype,devices
         lvr0            raid0  lvr0_rimage_0(0),lvr0_rimage_1(0)
         [lvr0_rimage_0] linear /dev/sda(...)
         [lvr0_rimage_1] linear /dev/sdb(...)

       raid1
       Each  rimage SubLV holds a complete copy of LV data.  No parity is used.  Each rmeta SubLV
       holds RAID metadata.

       # lvcreate --type raid1 --mirrors 1 --name lvr1 ...

       # lvs -a -o name,segtype,devices
         lvr1            raid1  lvr1_rimage_0(0),lvr1_rimage_1(0)
         [lvr1_rimage_0] linear /dev/sda(...)
         [lvr1_rimage_1] linear /dev/sdb(...)
         [lvr1_rmeta_0]  linear /dev/sda(...)
         [lvr1_rmeta_1]  linear /dev/sdb(...)

       raid4
       At least three rimage SubLVs each hold a portion of LV data and  one  rimage  SubLV  holds
       parity.  Each rmeta SubLV holds RAID metadata.

       # lvcreate --type raid4 --stripes 2 --name lvr4 ...

       # lvs -a -o name,segtype,devices
         lvr4            raid4  lvr4_rimage_0(0),\
                                lvr4_rimage_1(0),\
                                lvr4_rimage_2(0)
         [lvr4_rimage_0] linear /dev/sda(...)
         [lvr4_rimage_1] linear /dev/sdb(...)
         [lvr4_rimage_2] linear /dev/sdc(...)
         [lvr4_rmeta_0]  linear /dev/sda(...)
         [lvr4_rmeta_1]  linear /dev/sdb(...)
         [lvr4_rmeta_2]  linear /dev/sdc(...)

       raid5
       At  least  three  rimage  SubLVs  each typically hold a portion of LV data and parity (see
       section on raid5) Each rmeta SubLV holds RAID metadata.

       # lvcreate --type raid5 --stripes 2 --name lvr5 ...

       # lvs -a -o name,segtype,devices
         lvr5            raid5  lvr5_rimage_0(0),\
                                lvr5_rimage_1(0),\
                                lvr5_rimage_2(0)
         [lvr5_rimage_0] linear /dev/sda(...)
         [lvr5_rimage_1] linear /dev/sdb(...)
         [lvr5_rimage_2] linear /dev/sdc(...)
         [lvr5_rmeta_0]  linear /dev/sda(...)
         [lvr5_rmeta_1]  linear /dev/sdb(...)
         [lvr5_rmeta_2]  linear /dev/sdc(...)

       raid6
       At least five rimage SubLVs each typically hold a portion of LV  data  and  parity.   (see
       section on raid6) Each rmeta SubLV holds RAID metadata.

       # lvcreate --type raid6 --stripes 3 --name lvr6

       # lvs -a -o name,segtype,devices
         lvr6            raid6  lvr6_rimage_0(0),\
                                lvr6_rimage_1(0),\
                                lvr6_rimage_2(0),\
                                lvr6_rimage_3(0),\
                                lvr6_rimage_4(0),\
                                lvr6_rimage_5(0)
         [lvr6_rimage_0] linear /dev/sda(...)
         [lvr6_rimage_1] linear /dev/sdb(...)
         [lvr6_rimage_2] linear /dev/sdc(...)
         [lvr6_rimage_3] linear /dev/sdd(...)
         [lvr6_rimage_4] linear /dev/sde(...)
         [lvr6_rimage_5] linear /dev/sdf(...)
         [lvr6_rmeta_0]  linear /dev/sda(...)
         [lvr6_rmeta_1]  linear /dev/sdb(...)
         [lvr6_rmeta_2]  linear /dev/sdc(...)
         [lvr6_rmeta_3]  linear /dev/sdd(...)
         [lvr6_rmeta_4]  linear /dev/sde(...)
         [lvr6_rmeta_5]  linear /dev/sdf(...)

       raid10
       At  least  four  rimage  SubLVs  each hold a portion of LV data.  No parity is used.  Each
       rmeta SubLV holds RAID metadata.

       # lvcreate --type raid10 --stripes 2 --mirrors 1 --name lvr10

       # lvs -a -o name,segtype,devices
         lvr10            raid10 lvr10_rimage_0(0),\
                                 lvr10_rimage_1(0),\
                                 lvr10_rimage_2(0),\
                                 lvr10_rimage_3(0)
         [lvr10_rimage_0] linear /dev/sda(...)
         [lvr10_rimage_1] linear /dev/sdb(...)
         [lvr10_rimage_2] linear /dev/sdc(...)
         [lvr10_rimage_3] linear /dev/sdd(...)
         [lvr10_rmeta_0]  linear /dev/sda(...)
         [lvr10_rmeta_1]  linear /dev/sdb(...)
         [lvr10_rmeta_2]  linear /dev/sdc(...)
         [lvr10_rmeta_3]  linear /dev/sdd(...)

DEVICE FAILURE

       Physical devices in a RAID LV can fail or be lost for multiple reasons.  A device could be
       disconnected,  permanently  failed,  or temporarily disconnected.  The purpose of RAID LVs
       (levels 1 and higher) is to continue operating in a degraded mode, without losing LV data,
       even  after  a  device  fails.  The number of devices that can fail without the loss of LV
       data depends on the RAID level:
            • RAID0 (striped) LVs cannot tolerate losing any devices.  LV data will  be  lost  if
              any devices fail.
            • RAID1 LVs can tolerate losing all but one device without LV data loss.
            • RAID4 and RAID5 LVs can tolerate losing one device without LV data loss.
            • RAID6 LVs can tolerate losing two devices without LV data loss.
            • RAID10  is  variable,  and  depends  on  which devices are lost.  It stripes across
              multiple mirror groups with raid1 layout thus it can tolerate losing  all  but  one
              device in each of these groups without LV data loss.

       If a RAID LV is missing devices, or has other device-related problems, lvs reports this in
       the health_status (and attr) fields:

       lvs -o name,lv_health_status

       partial
              Devices are missing from the  LV.   This  is  also  indicated  by  the  letter  "p"
              (partial) in the 9th position of the lvs attr field.

       refresh needed
              A device was temporarily missing but has returned.  The LV needs to be refreshed to
              use the device again (which will usually require partial synchronization).  This is
              also  indicated  by  the letter "r" (refresh needed) in the 9th position of the lvs
              attr field.  See Refreshing an LV.  This could also indicate  a  problem  with  the
              device, in which case it should be be replaced, see Replacing Devices.

       mismatches exist
              See Scrubbing.

       Most commands will also print a warning if a device is missing, e.g.
       WARNING: Device for PV uItL3Z-wBME-DQy0-... not found or rejected ...

       This  warning  will  go away if the device returns or is removed from the VG (see vgreduce
       --removemissing).

   Activating an LV with missing devices
       A RAID LV that is missing devices may be activated or not, depending  on  the  "activation
       mode" used in lvchange:

       lvchange -ay --activationmode complete|degraded|partial LV

       complete
              The LV is only activated if all devices are present.

       degraded
              The  LV is activated with missing devices if the RAID level can tolerate the number
              of missing devices without LV data loss.

       partial
              The LV is always activated, even if portions of the LV data are missing because  of
              the  missing  device(s).   This  should only be used to perform extreme recovery or
              repair operations.

       Default activation mode when not specified by the command:
       lvm.conf(5) activation/activation_mode

       The default value is printed by:
       # lvmconfig --type default activation/activation_mode

   Replacing Devices
       Devices in a RAID LV can be replaced by other devices in the VG.  When  replacing  devices
       that  are no longer visible on the system, use lvconvert --repair.  When replacing devices
       that are still visible, use lvconvert --replace.   The  repair  command  will  attempt  to
       restore  the  same  number of data LVs that were previously in the LV.  The replace option
       can be repeated to replace multiple PVs.  Replacement devices  can  be  optionally  listed
       with either option.

       lvconvert --repair LV [NewPVs]

       lvconvert --replace OldPV LV [NewPV]

       lvconvert --replace OldPV1 --replace OldPV2 LV [NewPVs]

       New devices require synchronization with existing devices.
       See Synchronization.

   Refreshing an LV
       Refreshing  a  RAID  LV  clears  any  transient  device  failures  (device was temporarily
       disconnected) and returns the LV to its fully redundant mode.   Restoring  a  device  will
       usually  require at least partial synchronization (see Synchronization).  Failure to clear
       a transient failure results in the  RAID  LV  operating  in  degraded  mode  until  it  is
       reactivated.  Use the lvchange command to refresh an LV:

       lvchange --refresh LV

       # lvs -o name,vgname,segtype,attr,size vg
         LV VG   Type  Attr       LSize
         lv vg   raid1 Rwi-a-r-r- 100.00g

       # lvchange --refresh vg/lv

       # lvs -o name,vgname,segtype,attr,size vg
         LV VG   Type  Attr       LSize
         lv vg   raid1 Rwi-a-r--- 100.00g

   Automatic repair
       If  a  device  in  a  RAID  LV fails, device-mapper in the kernel notifies the dmeventd(8)
       monitoring process (see Monitoring).  dmeventd can be configured to automatically  respond
       using:
       lvm.conf(5) activation/raid_fault_policy

       Possible settings are:

       warn   A  warning  is  added  to the system log indicating that a device has failed in the
              RAID LV.  It is left to the user to repair the LV, e.g.  replace failed devices.

       allocate
              dmeventd automatically attempts to repair the LV using spare  devices  in  the  VG.
              Note  that  even  a  transient failure is treated as a permanent failure under this
              setting.  A new device is allocated and full synchronization is started.

       The specific command run by dmeventd(8) to warn or repair is:
       lvconvert --repair --use-policies LV

   Corrupted Data
       Data on a device can be corrupted due to hardware errors without  the  device  ever  being
       disconnected  or  there  being any fault in the software.  This should be rare, and can be
       detected (see Scrubbing).

   Rebuild specific PVs
       If specific PVs in a RAID LV are known to have corrupt data, the data on those PVs can  be
       reconstructed with:

       lvchange --rebuild PV LV

       The rebuild option can be repeated with different PVs to replace the data on multiple PVs.

DATA INTEGRITY

       The  device mapper integrity target can be used in combination with RAID levels 1,4,5,6,10
       to detect and correct data corruption in RAID images. A dm-integrity layer is placed above
       each  RAID  image,  and  an  extra  sub  LV  is  created  to hold integrity metadata (data
       checksums) for each RAID image.  When data is read from an image, integrity checksums  are
       used  to  detect corruption. If detected, dm-raid reads the data from another (good) image
       to return to the caller.  dm-raid will also automatically write the good data back to  the
       image with bad data to correct the corruption.

       When  creating  a  RAID  LV  with  integrity,  or  adding integrity, space is required for
       integrity metadata.  Every 500MB of LV data requires an additional 4MB to be allocated for
       integrity metadata, for each RAID image.

       Create a RAID LV with integrity:
       lvcreate --type raidN --raidintegrity y

       Add integrity to an existing RAID LV:
       lvconvert --raidintegrity y LV

       Remove integrity from a RAID LV:
       lvconvert --raidintegrity n LV

   Integrity options
       --raidintegritymode journal|bitmap
              Use  a  journal  (default)  or bitmap for keeping integrity checksums consistent in
              case of a crash. The bitmap areas are recalculated after a crash, so corruption  in
              those  areas  would  not  be  detected.  A journal does not have this problem.  The
              journal mode doubles writes to storage, but can improve performance  for  scattered
              writes  packed into a single journal write.  bitmap mode can in theory achieve full
              write throughput of the device, but would not benefit from the potential  scattered
              write optimization.

       --raidintegrityblocksize 512|1024|2048|4096
              The  block  size  to use for dm-integrity on raid images.  The integrity block size
              should usually match the device logical block size, or the file system sector/block
              sizes.   It  may  be less than the file system sector/block size, but not less than
              the device logical block size.  Possible values: 512, 1024, 2048, 4096.

   Integrity initialization
       When integrity is added to an LV, the kernel needs to initialize  the  integrity  metadata
       (checksums)  for  all  blocks  in  the  LV.  The data corruption checking performed by dm-
       integrity will only operate on areas of the LV that are already initialized.  The progress
       of integrity initialization is reported by the "syncpercent" LV reporting field (and under
       the Cpy%Sync lvs column.)

   Integrity limitations
       To work around some limitations, it is possible to remove integrity from the LV, make  the
       change,  then  add  integrity  again.   (Integrity metadata would need to initialized when
       added again.)

       LVM must be able to allocate the integrity metadata sub LV on a single PV that is  already
       in  use by the associated RAID image. This can potentially cause a problem during lvextend
       if the original PV holding the image and integrity metadata is full.  To work around  this
       limitation, remove integrity, extend the LV, and add integrity again.

       Additional RAID images can be added to raid1 LVs, but not to other raid levels.

       A raid1 LV with integrity cannot be converted to linear (remove integrity to do this.)

       RAID LVs with integrity cannot yet be used as sub LVs with other LV types.

       The  following  are  not  yet  permitted  on  RAID  LVs  with integrity: lvreduce, pvmove,
       snapshots, splitmirror, raid syncaction commands, raid rebuild.

RAID1 TUNING

       A RAID1 LV can be tuned so that certain devices are avoided for reading while all  devices
       are still written to.

       lvchange --[raid]writemostly PV[:y|n|t] LV

       The  specified device will be marked as "write mostly", which means that reading from this
       device will be avoided, and other devices will be preferred for reading (unless  no  other
       devices are available.)  This minimizes the I/O to the specified device.

       If  the  PV name has no suffix, the write mostly attribute is set.  If the PV name has the
       suffix :n, the write mostly attribute is cleared, and the suffix :t  toggles  the  current
       setting.

       The  write mostly option can be repeated on the command line to change multiple devices at
       once.

       To report the current write mostly setting, the lvs attr field will show the letter "w" in
       the 9th position when write mostly is set:

       lvs -a -o name,attr

       When  a  device  is  marked write mostly, the maximum number of outstanding writes to that
       device can be configured.  Once the maximum is reached, further writes become synchronous.
       When  synchronous,  a  write  to  the  LV will not complete until writes to all the mirror
       images are complete.

       lvchange --[raid]writebehind Number LV

       To report the current write behind setting, run:

       lvs -o name,raid_write_behind

       When write behind is not configured, or set to 0, all LV writes are synchronous.

RAID TAKEOVER

       RAID takeover is converting a RAID LV from one RAID  level  to  another,  e.g.   raid5  to
       raid6.   Changing  the  RAID  level  is usually done to increase or decrease resilience to
       device failures or to restripe LVs.  This is done using lvconvert and specifying  the  new
       RAID level as the LV type:

       lvconvert --type RaidLevel LV [PVs]

       The most common and recommended RAID takeover conversions are:

       linear to raid1
              Linear is a single image of LV data, and converting it to raid1 adds a mirror image
              which is a direct copy of the original linear image.

       striped/raid0 to raid4/5/6
              Adding parity devices to a striped volume results in raid4/5/6.

       Unnatural conversions that are not recommended include converting between striped and non-
       striped  types.   This is because file systems often optimize I/O patterns based on device
       striping values.  If those values change, it can decrease performance.

       Converting to a higher RAID level requires allocating new SubLVs to  hold  RAID  metadata,
       and  new  SubLVs  to  hold  parity  blocks  for LV data.  Converting to a lower RAID level
       removes the SubLVs that are no longer needed.

       Conversion often requires full synchronization  of  the  RAID  LV  (see  Synchronization).
       Converting  to  RAID1  requires copying all LV data blocks to N new images on new devices.
       Converting to a parity RAID level requires reading all LV data blocks, calculating parity,
       and  writing the new parity blocks.  Synchronization can take a long time depending on the
       throughpout of the devices used and the size of the RaidLV.  It can  degrade  performance.
       Rate controls also apply to conversion; see --minrecoveryrate and --maxrecoveryrate.

       Warning: though it is possible to create striped LVs  with up to 128 stripes, a maximum of
       64 stripes can be converted to raid0, 63 to raid4/5 and 62 to raid6 because of  the  added
       parity SubLVs.  A striped LV with a maximum of 32 stripes can be converted to raid10.

       The following takeover conversions are currently possible:
            • between striped and raid0.
            • between linear and raid1.
            • between mirror and raid1.
            • between raid1 with two images and raid4/5.
            • between striped/raid0 and raid4.
            • between striped/raid0 and raid5.
            • between striped/raid0 and raid6.
            • between raid4 and raid5.
            • between raid4/raid5 and raid6.
            • between striped/raid0 and raid10.
            • between striped and raid4.

   Indirect conversions
       Converting  from one raid level to another may require multiple steps, converting first to
       intermediate raid levels.

       linear to raid6

       To convert an LV from linear to raid6:
       1. convert to raid1 with two images
       2. convert to raid5 (internally raid5_ls) with two images
       3. convert to raid5 with three or more stripes (reshape)
       4. convert to raid6 (internally raid6_ls_6)
       5. convert to raid6 (internally raid6_zr, reshape)

       The commands to perform the steps above are:
       1. lvconvert --type raid1 --mirrors 1 LV
       2. lvconvert --type raid5 LV
       3. lvconvert --stripes 3 LV
       4. lvconvert --type raid6 LV
       5. lvconvert --type raid6 LV

       The final  conversion  from  raid6_ls_6  to  raid6_zr  is  done  to  avoid  the  potential
       write/recovery performance reduction in raid6_ls_6 because of the dedicated parity device.
       raid6_zr rotates data and parity blocks to avoid this.

       linear to striped

       To convert an LV from linear to striped:
       1. convert to raid1 with two images
       2. convert to raid5_n
       3. convert to raid5_n with five 128k stripes (reshape)
       4. convert raid5_n to striped

       The commands to perform the steps above are:
       1. lvconvert --type raid1 --mirrors 1 LV
       2. lvconvert --type raid5_n LV
       3. lvconvert --stripes 5 --stripesize 128k LV
       4. lvconvert --type striped LV

       The raid5_n type in step 2 is used because it has dedicated parity SubLVs at the end,  and
       can be converted to striped directly.  The stripe size is increased in step 3 to add extra
       space for the conversion process.  This step grows the LV size by a factor of five.  After
       conversion,  this  extra  space  can be reduced (or used to grow the file system using the
       LV).

       Reversing these steps will convert a striped LV to linear.

       raid6 to striped

       To convert an LV from raid6_nr to striped:
       1. convert to raid6_n_6
       2. convert to striped

       The commands to perform the steps above are:
       1. lvconvert --type raid6_n_6 LV
       2. lvconvert --type striped LV

       Examples

       Converting an LV from linear to raid1.

       # lvs -a -o name,segtype,size vg
         LV   Type   LSize
         lv   linear 300.00g

       # lvconvert --type raid1 --mirrors 1 vg/lv

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            raid1  300.00g
         [lv_rimage_0] linear 300.00g
         [lv_rimage_1] linear 300.00g
         [lv_rmeta_0]  linear   3.00m
         [lv_rmeta_1]  linear   3.00m

       Converting an LV from mirror to raid1.

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            mirror 100.00g
         [lv_mimage_0] linear 100.00g
         [lv_mimage_1] linear 100.00g
         [lv_mlog]     linear   3.00m

       # lvconvert --type raid1 vg/lv

       # lvs -a -o name,segtype,size vg
         LV            Type   LSize
         lv            raid1  100.00g
         [lv_rimage_0] linear 100.00g
         [lv_rimage_1] linear 100.00g
         [lv_rmeta_0]  linear   3.00m
         [lv_rmeta_1]  linear   3.00m

       Converting an LV from linear to raid1 (with 3 images).

       # lvconvert --type raid1 --mirrors 2 vg/lv

       Converting an LV from striped (with 4 stripes) to raid6_n_6.

       # lvcreate --stripes 4 -L64M -n lv vg

       # lvconvert --type raid6 vg/lv

       # lvs -a -o lv_name,segtype,sync_percent,data_copies
         LV            Type      Cpy%Sync #Cpy
         lv            raid6_n_6 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       This convert begins by allocating MetaLVs  (rmeta_#)  for  each  of  the  existing  stripe
       devices.   It  then  creates  2  additional  MetaLV/DataLV  pairs  (rmeta_#/rimage_#)  for
       dedicated raid6 parity.

       If rotating data/parity is required, such as with raid6_nr, it must be done  by  reshaping
       (see below).

RAID RESHAPING

       RAID  reshaping  is  changing  attributes  of a RAID LV while keeping the same RAID level.
       This includes changing RAID layout, stripe size, or number of stripes.

       When changing the RAID layout or stripe size, no new SubLVs (MetaLVs or DataLVs)  need  to
       be  allocated, but DataLVs are extended by a small amount (typically 1 extent).  The extra
       space allows blocks in a stripe to be updated safely, and not be corrupted in  case  of  a
       crash.  If a crash occurs, reshaping can just be restarted.

       (If  blocks  in a stripe were updated in place, a crash could leave them partially updated
       and corrupted.  Instead, an existing stripe is quiesced, read, changed in layout, and  the
       new  stripe  written  to  free space.  Once that is done, the new stripe is unquiesced and
       used.)

       Examples
       (Command output shown in examples may change.)

       Converting raid6_n_6 to raid6_nr with rotating data/parity.

       This conversion naturally follows a previous conversion from  striped/raid0  to  raid6_n_6
       (shown above).  It completes the transition to a more traditional RAID6.

       # lvs -o lv_name,segtype,sync_percent,data_copies
         LV            Type      Cpy%Sync #Cpy
         lv            raid6_n_6 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       # lvconvert --type raid6_nr vg/lv

       # lvs -a -o lv_name,segtype,sync_percent,data_copies
         LV            Type     Cpy%Sync #Cpy
         lv            raid6_nr 100.00      3
         [lv_rimage_0] linear
         [lv_rimage_0] linear
         [lv_rimage_1] linear
         [lv_rimage_1] linear
         [lv_rimage_2] linear
         [lv_rimage_2] linear
         [lv_rimage_3] linear
         [lv_rimage_3] linear
         [lv_rimage_4] linear
         [lv_rimage_5] linear
         [lv_rmeta_0]  linear
         [lv_rmeta_1]  linear
         [lv_rmeta_2]  linear
         [lv_rmeta_3]  linear
         [lv_rmeta_4]  linear
         [lv_rmeta_5]  linear

       The  DataLVs are larger (additional segment in each) which provides space for out-of-place
       reshaping.  The result is:

       # lvs -a -o lv_name,segtype,seg_pe_ranges,dataoffset
         LV            Type     PE Ranges          DOff
         lv            raid6_nr lv_rimage_0:0-32 \
                                lv_rimage_1:0-32 \
                                lv_rimage_2:0-32 \
                                lv_rimage_3:0-32
         [lv_rimage_0] linear   /dev/sda:0-31      2048
         [lv_rimage_0] linear   /dev/sda:33-33
         [lv_rimage_1] linear   /dev/sdaa:0-31     2048
         [lv_rimage_1] linear   /dev/sdaa:33-33
         [lv_rimage_2] linear   /dev/sdab:1-33     2048
         [lv_rimage_3] linear   /dev/sdac:1-33     2048
         [lv_rmeta_0]  linear   /dev/sda:32-32
         [lv_rmeta_1]  linear   /dev/sdaa:32-32
         [lv_rmeta_2]  linear   /dev/sdab:0-0
         [lv_rmeta_3]  linear   /dev/sdac:0-0

       All segments  with  PE  ranges  '33-33'  provide  the  out-of-place  reshape  space.   The
       dataoffset  column  shows that the data was moved from initial offset 0 to 2048 sectors on
       each component DataLV.

       For performance reasons the raid6_nr RaidLV can  be  restriped.   Convert  it  from  3-way
       striped to 5-way-striped.

       # lvconvert --stripes 5 vg/lv
         Using default stripesize 64.00 KiB.
         WARNING: Adding stripes to active logical volume vg/lv will \
         grow it from 99 to 165 extents!
         Run "lvresize -l99 vg/lv" to shrink it or use the additional \
         capacity.
         Logical volume vg/lv successfully converted.

       # lvs vg/lv
         LV   VG     Attr       LSize   Cpy%Sync
         lv   vg     rwi-a-r-s- 652.00m 52.94

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33 \
                                           lv_rimage_6:0-33   0
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      0
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     0
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     0
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     0
         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     0
         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     0
         [lv_rimage_6] iwi-aor--- linear   /dev/sdaf:1-34     0
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor--- linear   /dev/sdaf:0-0

       Stripes  also  can  be removed from raid5 and 6.  Convert the 5-way striped raid6_nr LV to
       4-way-striped.  The force option needs to be used, because removing  stripes  (i.e.  image
       SubLVs) from a RaidLV will shrink its size.

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         WARNING: Removing stripes from active logical volume vg/lv will \
         shrink it from 660.00 MiB to 528.00 MiB!
         THIS MAY DESTROY (PARTS OF) YOUR DATA!
         If that leaves the logical volume larger than 206 extents due \
         to stripe rounding,
         you may want to grow the content afterwards (filesystem etc.)
         WARNING: to remove freed stripes after the conversion has finished,\
         you have to run "lvconvert --stripes 4 vg/lv"
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r-s- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33 \
                                           lv_rimage_6:0-33   0
         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:0-32      0
         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:0-32     0
         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:0-32     0
         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] Iwi-aor--- linear   /dev/sdac:1-34     0
         [lv_rimage_4] Iwi-aor--- linear   /dev/sdad:1-34     0
         [lv_rimage_5] Iwi-aor--- linear   /dev/sdae:1-34     0
         [lv_rimage_6] Iwi-aor-R- linear   /dev/sdaf:1-34     0
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor-R- linear   /dev/sdaf:0-0

       The  's'  in column 9 of the attribute field shows the RaidLV is still reshaping.  The 'R'
       in the same column of the attribute field shows the freed image Sub LVs  which  will  need
       removing once the reshaping finished.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type     PE Ranges          DOff
         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
                                  lv_rimage_1:0-33 \
                                  lv_rimage_2:0-33 ... \
                                  lv_rimage_5:0-33 \
                                  lv_rimage_6:0-33   8192

       Now  that  the  reshape  is  finished  the 'R' attribute on the RaidLV shows images can be
       removed.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type     PE Ranges          DOff
         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
                                  lv_rimage_1:0-33 \
                                  lv_rimage_2:0-33 ... \
                                  lv_rimage_5:0-33 \
                                  lv_rimage_6:0-33   8192

       This is achieved by  repeating  the  command  ("lvconvert  --stripes  4  vg/lv"  would  be
       sufficient).

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV            Attr       Type     PE Ranges          DOff
         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
                                           lv_rimage_1:0-33 \
                                           lv_rimage_2:0-33 ... \
                                           lv_rimage_5:0-33   8192
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      8192
         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     8192
         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     8192
         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     8192
         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     8192
         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     8192
         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0

       # lvs -a -o lv_name,attr,segtype,reshapelen vg
         LV            Attr       Type     RSize
         lv            rwi-a-r--- raid6_nr 24.00m
         [lv_rimage_0] iwi-aor--- linear    4.00m
         [lv_rimage_0] iwi-aor--- linear
         [lv_rimage_1] iwi-aor--- linear    4.00m
         [lv_rimage_1] iwi-aor--- linear
         [lv_rimage_2] iwi-aor--- linear    4.00m
         [lv_rimage_2] iwi-aor--- linear
         [lv_rimage_3] iwi-aor--- linear    4.00m
         [lv_rimage_4] iwi-aor--- linear    4.00m
         [lv_rimage_5] iwi-aor--- linear    4.00m
         [lv_rmeta_0]  ewi-aor--- linear
         [lv_rmeta_1]  ewi-aor--- linear
         [lv_rmeta_2]  ewi-aor--- linear
         [lv_rmeta_3]  ewi-aor--- linear
         [lv_rmeta_4]  ewi-aor--- linear
         [lv_rmeta_5]  ewi-aor--- linear

       Future developments might include automatic removal of the freed images.

       If the reshape space shall be removed any lvconvert command not changing the layout can be
       used:

       # lvconvert --stripes 4 vg/lv
         Using default stripesize 64.00 KiB.
         No change in RAID LV vg/lv layout, freeing reshape space.
         Logical volume vg/lv successfully converted.

       # lvs -a -o lv_name,attr,segtype,reshapelen vg
         LV            Attr       Type     RSize
         lv            rwi-a-r--- raid6_nr    0
         [lv_rimage_0] iwi-aor--- linear      0
         [lv_rimage_0] iwi-aor--- linear
         [lv_rimage_1] iwi-aor--- linear      0
         [lv_rimage_1] iwi-aor--- linear
         [lv_rimage_2] iwi-aor--- linear      0
         [lv_rimage_2] iwi-aor--- linear
         [lv_rimage_3] iwi-aor--- linear      0
         [lv_rimage_4] iwi-aor--- linear      0
         [lv_rimage_5] iwi-aor--- linear      0
         [lv_rmeta_0]  ewi-aor--- linear
         [lv_rmeta_1]  ewi-aor--- linear
         [lv_rmeta_2]  ewi-aor--- linear
         [lv_rmeta_3]  ewi-aor--- linear
         [lv_rmeta_4]  ewi-aor--- linear
         [lv_rmeta_5]  ewi-aor--- linear

       In case the RaidLV should be converted to striped:

       # lvconvert --type striped vg/lv
         Unable to convert LV vg/lv from raid6_nr to striped.
         Converting vg/lv from raid6_nr is directly possible to the \
         following layouts:
           raid6_nc
           raid6_zr
           raid6_la_6
           raid6_ls_6
           raid6_ra_6
           raid6_rs_6
           raid6_n_6

       A direct conversion isn't possible thus the command  informed  about  the  possible  ones.
       raid6_n_6  is  suitable  to  convert  to striped so convert to it first (this is a reshape
       changing the raid6 layout from raid6_nr to raid6_n_6).

       # lvconvert --type raid6_n_6
         Using default stripesize 64.00 KiB.
         Converting raid6_nr LV vg/lv to raid6_n_6.
       Are you sure you want to convert raid6_nr LV vg/lv? [y/n]: y
         Logical volume vg/lv successfully converted.

       Wait for the reshape to finish.

       # lvconvert --type striped vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type    PE Ranges  DOff
         lv   -wi-a----- striped /dev/sda:2-32 \
                                 /dev/sdaa:2-32 \
                                 /dev/sdab:2-32 \
                                 /dev/sdac:3-33
         lv   -wi-a----- striped /dev/sda:34-35 \
                                 /dev/sdaa:34-35 \
                                 /dev/sdab:34-35 \
                                 /dev/sdac:34-35

       From striped we can convert to raid10

       # lvconvert --type raid10 vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         LV   Attr       Type   PE Ranges          DOff
         lv   rwi-a-r--- raid10 lv_rimage_0:0-32 \
                                lv_rimage_4:0-32 \
                                lv_rimage_1:0-32 ... \
                                lv_rimage_3:0-32 \
                                lv_rimage_7:0-32   0

       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
         WARNING: Cannot find matching striped segment for vg/lv_rimage_3.
         LV            Attr       Type   PE Ranges          DOff
         lv            rwi-a-r--- raid10 lv_rimage_0:0-32 \
                                         lv_rimage_4:0-32 \
                                         lv_rimage_1:0-32 ... \
                                         lv_rimage_3:0-32 \
                                         lv_rimage_7:0-32   0
         [lv_rimage_0] iwi-aor--- linear /dev/sda:2-32      0
         [lv_rimage_0] iwi-aor--- linear /dev/sda:34-35
         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:2-32     0
         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:34-35
         [lv_rimage_2] iwi-aor--- linear /dev/sdab:2-32     0
         [lv_rimage_2] iwi-aor--- linear /dev/sdab:34-35
         [lv_rimage_3] iwi-XXr--- linear /dev/sdac:3-35     0
         [lv_rimage_4] iwi-aor--- linear /dev/sdad:1-33     0
         [lv_rimage_5] iwi-aor--- linear /dev/sdae:1-33     0
         [lv_rimage_6] iwi-aor--- linear /dev/sdaf:1-33     0
         [lv_rimage_7] iwi-aor--- linear /dev/sdag:1-33     0
         [lv_rmeta_0]  ewi-aor--- linear /dev/sda:0-0
         [lv_rmeta_1]  ewi-aor--- linear /dev/sdaa:0-0
         [lv_rmeta_2]  ewi-aor--- linear /dev/sdab:0-0
         [lv_rmeta_3]  ewi-aor--- linear /dev/sdac:0-0
         [lv_rmeta_4]  ewi-aor--- linear /dev/sdad:0-0
         [lv_rmeta_5]  ewi-aor--- linear /dev/sdae:0-0
         [lv_rmeta_6]  ewi-aor--- linear /dev/sdaf:0-0
         [lv_rmeta_7]  ewi-aor--- linear /dev/sdag:0-0

       raid10 allows to add stripes but can't remove them.

       A more elaborate example to convert from linear to striped  with  interim  conversions  to
       raid1 then raid5 followed by restripe (4 steps).

       We start with the linear LV.

       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV   LSize   Type   Cpy%Sync #DStr Stripe RSize Devices
         lv   128.00m linear              1     0        /dev/sda(0)

       Then convert it to a 2-way raid1.

       # lvconvert --mirrors 1 vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV            LSize   Type   #DStr Stripe RSize Devices
         lv            128.00m raid1      2     0        lv_rimage_0(0),\
                                                         lv_rimage_1(0)
         [lv_rimage_0] 128.00m linear     1     0        /dev/sda(0)
         [lv_rimage_1] 128.00m linear     1     0        /dev/sdhx(1)
         [lv_rmeta_0]    4.00m linear     1     0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear     1     0        /dev/sdhx(0)

       Once the raid1 LV is fully synchronized we convert it to raid5_n (only 2-way raid1 LVs can
       be converted to raid5).  We select raid5_n here because it has dedicated parity SubLVs  at
       the end and can be converted to striped directly without any additional conversion.

       # lvconvert --type raid5_n vg/lv
         Using default stripesize 64.00 KiB.
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV            LSize   Type    #DStr Stripe RSize Devices
         lv            128.00m raid5_n     1 64.00k     0 lv_rimage_0(0),\
                                                          lv_rimage_1(0)
         [lv_rimage_0] 128.00m linear      1     0      0 /dev/sda(0)
         [lv_rimage_1] 128.00m linear      1     0      0 /dev/sdhx(1)
         [lv_rmeta_0]    4.00m linear      1     0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear      1     0        /dev/sdhx(0)

       Now  we'll  change  the number of data stripes from 1 to 5 and request 128K stripe size in
       one command.  This will grow the size of the LV by a factor of 5 (we add 4 data stripes to
       the  one  given).   That  additional  space  can  be  used  by  e.g. growing any contained
       filesystem or the LV can be reduced in size after the reshaping conversion has finished.

       # lvconvert --stripesize 128k --stripes 5 vg/lv
         Converting stripesize 64.00 KiB of raid5_n LV vg/lv to 128.00 KiB.
         WARNING: Adding stripes to active logical volume vg/lv will grow \
         it from 32 to 160 extents!
         Run "lvresize -l32 vg/lv" to shrink it or use the additional capacity.
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices
         LV            LSize   Type    #DStr Stripe  RSize Devices
         lv            640.00m raid5_n     5 128.00k     6 lv_rimage_0(0),\
                                                           lv_rimage_1(0),\
                                                           lv_rimage_2(0),\
                                                           lv_rimage_3(0),\
                                                           lv_rimage_4(0),\
                                                           lv_rimage_5(0)
         [lv_rimage_0] 132.00m linear      1      0      1 /dev/sda(33)
         [lv_rimage_0] 132.00m linear      1      0        /dev/sda(0)
         [lv_rimage_1] 132.00m linear      1      0      1 /dev/sdhx(33)
         [lv_rimage_1] 132.00m linear      1      0        /dev/sdhx(1)
         [lv_rimage_2] 132.00m linear      1      0      1 /dev/sdhw(33)
         [lv_rimage_2] 132.00m linear      1      0        /dev/sdhw(1)
         [lv_rimage_3] 132.00m linear      1      0      1 /dev/sdhv(33)
         [lv_rimage_3] 132.00m linear      1      0        /dev/sdhv(1)
         [lv_rimage_4] 132.00m linear      1      0      1 /dev/sdhu(33)
         [lv_rimage_4] 132.00m linear      1      0        /dev/sdhu(1)
         [lv_rimage_5] 132.00m linear      1      0      1 /dev/sdht(33)
         [lv_rimage_5] 132.00m linear      1      0        /dev/sdht(1)
         [lv_rmeta_0]    4.00m linear      1      0        /dev/sda(32)
         [lv_rmeta_1]    4.00m linear      1      0        /dev/sdhx(0)
         [lv_rmeta_2]    4.00m linear      1      0        /dev/sdhw(0)
         [lv_rmeta_3]    4.00m linear      1      0        /dev/sdhv(0)
         [lv_rmeta_4]    4.00m linear      1      0        /dev/sdhu(0)
         [lv_rmeta_5]    4.00m linear      1      0        /dev/sdht(0)

       Once the conversion has finished we can can convert to striped.

       # lvconvert --type striped vg/lv
         Logical volume vg/lv successfully converted.

       # lvs -a -o name,size,segtype,datastripes,\
                   stripesize,reshapelenle,devices vg
         LV   LSize   Type    #DStr Stripe  RSize Devices
         lv   640.00m striped     5 128.00k       /dev/sda(33),\
                                                  /dev/sdhx(33),\
                                                  /dev/sdhw(33),\
                                                  /dev/sdhv(33),\
                                                  /dev/sdhu(33)
         lv   640.00m striped     5 128.00k       /dev/sda(0),\
                                                  /dev/sdhx(1),\
                                                  /dev/sdhw(1),\
                                                  /dev/sdhv(1),\
                                                  /dev/sdhu(1)

       Reversing these steps will convert a given striped LV to linear.

       Mind the facts that stripes are removed thus the capacity of the RaidLV  will  shrink  and
       that changing the RaidLV layout will influence its performance.

       "lvconvert  --stripes  1  vg/lv"  for converting to 1 stripe will inform upfront about the
       reduced size to allow for resizing the content  or  growing  the  RaidLV  before  actually
       converting to 1 stripe.  The --force option is needed to allow stripe removing conversions
       to prevent data loss.

       Of course any interim step can be the intended last one (e.g. striped → raid1).

RAID5 VARIANTS

       raid5_ls
            • RAID5 left symmetric
            • Rotating parity N with data restart

       raid5_la
            • RAID5 left asymmetric
            • Rotating parity N with data continuation

       raid5_rs
            • RAID5 right symmetric
            • Rotating parity 0 with data restart

       raid5_ra
            • RAID5 right asymmetric
            • Rotating parity 0 with data continuation

       raid5_n
            • RAID5 parity n
            • Dedicated parity device n used for striped/raid0 conversions
            • Used for RAID Takeover

RAID6 VARIANTS

       raid6
            • RAID6 zero restart (aka left symmetric)
            • Rotating parity 0 with data restart
            • Same as raid6_zr

       raid6_zr
            • RAID6 zero restart (aka left symmetric)
            • Rotating parity 0 with data restart

       raid6_nr
            • RAID6 N restart (aka right symmetric)
            • Rotating parity N with data restart

       raid6_nc
            • RAID6 N continue
            • Rotating parity N with data continuation

       raid6_n_6
            • RAID6 last parity devices
            • Fixed dedicated last devices (P-Syndrome N-1 and Q-Syndrome N)  with  striped  data
              used for striped/raid0 conversions
            • Used for RAID Takeover

       raid6_{ls,rs,la,ra}_6
            • RAID6 last parity device
            • Dedicated last parity device used for conversions from/to raid5_{ls,rs,la,ra}

       raid6_ls_6
            • RAID6 N continue
            • Same as raid5_ls for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

       raid6_la_6
            • RAID6 N continue
            • Same as raid5_la for N-1 devices with fixed Q-Syndrome N
            • Used forRAID Takeover

       raid6_rs_6
            • RAID6 N continue
            • Same as raid5_rs for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

       raid6_ra_6
            • RAID6 N continue
            • Same as raid5_ra for N-1 devices with fixed Q-Syndrome N
            • Used for RAID Takeover

HISTORY

       The  2.6.38-rc1 version of the Linux kernel introduced a device-mapper target to interface
       with the software RAID (MD) personalities.  This provided device-mapper  with  RAID  4/5/6
       capabilities  and  a  larger development community.  Later, support for RAID1, RAID10, and
       RAID1E (RAID 10 variants) were added.  Support for these new kernel RAID targets was added
       to  LVM  version  2.02.87.   The capabilities of the LVM raid1 type have surpassed the old
       mirror type.  raid1 is now recommended instead of mirror.  raid1 became  the  default  for
       mirroring in LVM version 2.02.100.

SEE ALSO

       lvm(8), lvm.conf(5), lvcreate(8), lvconvert(8), lvchange(8), lvextend(8), dmeventd(8)