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6.8. Creating a RAID LV with DM integrity

When you create a RAID LV with device mapper (DM) integrity or add integrity to an existing RAID LV, it mitigates the risk of losing data due to soft corruption. Wait for the integrity synchronization and the RAID metadata to complete before using the LV. Otherwise, the background initialization might impact the LV’s performance.

Procédure

  1. Create a RAID LV with DM integrity. The following example creates a new RAID LV with integrity named test-lv in the my_vg volume group, with a usable size of 256M and RAID level 1: 

    # lvcreate --type raid1 --raidintegrity y -L 256M -n test-lv my_vg
Creating integrity metadata LV test-lv_rimage_0_imeta with size 8.00 MiB.
Logical volume "test-lv_rimage_0_imeta" created.
Creating integrity metadata LV test-lv_rimage_1_imeta with size 8.00 MiB.
Logical volume "test-lv_rimage_1_imeta" created.
Logical volume "test-lv" created.
    Copy to Clipboard Toggle word wrap
    Note

    To add DM integrity to an existing RAID LV, use the following command: 

    # lvconvert --raidintegrity y my_vg/test-lv
    Copy to Clipboard Toggle word wrap

    Adding integrity to a RAID LV limits the number of operations that you can perform on that RAID LV.

  2. Optional: Remove the integrity before performing certain operations. 

    # lvconvert --raidintegrity n my_vg/test-lv
Logical volume my_vg/test-lv has removed integrity.
    Copy to Clipboard Toggle word wrap

Vérification

  • View information about the added DM integrity:

    • View information about the test-lv RAID LV that was created in the my_vg volume group: 

      # lvs -a my_vg
  LV                        VG      Attr       LSize   Origin                 Cpy%Sync
  test-lv                   my_vg rwi-a-r--- 256.00m                          2.10
  [test-lv_rimage_0]        my_vg gwi-aor--- 256.00m [test-lv_rimage_0_iorig] 93.75
  [test-lv_rimage_0_imeta]  my_vg ewi-ao----   8.00m
  [test-lv_rimage_0_iorig]  my_vg -wi-ao---- 256.00m
  [test-lv_rimage_1]        my_vg gwi-aor--- 256.00m [test-lv_rimage_1_iorig] 85.94
 [...]
      Copy to Clipboard Toggle word wrap

      The following describes different options from this output:

      g attribute
      It is the list of attributes under the Attr column indicates that the RAID image is using integrity. The integrity stores the checksums in the _imeta RAID LV.
      Cpy%Sync column
      It indicates the synchronization progress for both the top level RAID LV and for each RAID image.
      RAID image
      It is is indicated in the LV column by raid_image_N.
      LV column
      It ensures that the synchronization progress displays 100% for the top level RAID LV and for each RAID image.

    • Display the type for each RAID LV: 

      # lvs -a my-vg -o+segtype
  LV                       VG      Attr       LSize   Origin                 Cpy%Sync Type
  test-lv                  my_vg rwi-a-r--- 256.00m                          87.96    raid1
  [test-lv_rimage_0]       my_vg gwi-aor--- 256.00m [test-lv_rimage_0_iorig] 100.00   integrity
  [test-lv_rimage_0_imeta] my_vg ewi-ao----   8.00m                                   linear
  [test-lv_rimage_0_iorig] my_vg -wi-ao---- 256.00m                                   linear
  [test-lv_rimage_1]       my_vg gwi-aor--- 256.00m [test-lv_rimage_1_iorig] 100.00   integrity
 [...]
      Copy to Clipboard Toggle word wrap

    • There is an incremental counter that counts the number of mismatches detected on each RAID image. View the data mismatches detected by integrity from rimage_0 under my_vg/test-lv: 

      # lvs -o+integritymismatches my_vg/test-lv_rimage_0
  LV                 VG      Attr       LSize   Origin                    Cpy%Sync IntegMismatches
  [test-lv_rimage_0] my_vg gwi-aor--- 256.00m [test-lv_rimage_0_iorig]    100.00                 0
      Copy to Clipboard Toggle word wrap

      In this example, the integrity has not detected any data mismatches and thus the IntegMismatches counter shows zero (0).

    • View the data integrity information in the /var/log/messages log files, as shown in the following examples:

      Exemple 6.1. Example of dm-integrity mismatches from the kernel message logs

      device-mapper: integrity: dm-12: Checksum failed at sector 0x24e7

      Exemple 6.2. Example of dm-integrity data corrections from the kernel message logs

      md/raid1:mdX: read error corrected (8 sectors at 9448 on dm-16)

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