Home > Storage > PowerVault > Guides > Dell PowerVault ME5 Series and Linux > Mounting snapshots to recover data
Snapshots are useful to recover data that is deleted, corrupted, or changed unintentionally on the source volumes. Mount a snapshot created before the unintentional change happened on an alternate host and retrieve the data using the appropriate tools, such as cp, dd, or application-specific utilities. If data resides on multiple volumes, the corresponding snapshots of the volumes must be made available to the host.
To retrieve data from the snapshot volumes, it is recommended to mount snapshots on an alternate host instead of on the source host. If the snapshots are attached to the source host, additional steps are necessary to mount the snapshots because the metadata on the snapshot volumes is the same as the source volumes. This metadata, such as disk label, UUID, and volume group metadata, conflicts with existing mounted volumes.
Use the following procedures to modify the metadata on the snapshots. The snapshot volumes need to be attached to the host with read-write access.
# rescan-scsi-bus.sh -a
# lsscsi -is |grep -i 3600c0ff00064639b98197e6301000000
[11:0:10:2] disk DellEMC ME5 I200 /dev/sdz 3600c0ff00064639b98197e6301000000 399GB
[11:0:11:2] disk DellEMC ME5 I200 /dev/sdaa 3600c0ff00064639b98197e6301000000 399GB
[11:0:12:2] disk DellEMC ME5 I200 /dev/sdab 3600c0ff00064639b98197e6301000000 399GB
[11:0:13:2] disk DellEMC ME5 I200 /dev/sdac 3600c0ff00064639b98197e6301000000 399GB
[12:0:10:2] disk DellEMC ME5 I200 /dev/sdad 3600c0ff00064639b98197e6301000000 399GB
[12:0:11:2] disk DellEMC ME5 I200 /dev/sdae 3600c0ff00064639b98197e6301000000 399GB
[12:0:12:2] disk DellEMC ME5 I200 /dev/sdaf 3600c0ff00064639b98197e6301000000 399GB
[12:0:13:2] disk DellEMC ME5 I200 /dev/sdag 3600c0ff00064639b98197e6301000000 399GB
# multipath -l
mpathh (3600c0ff00064639b98197e6301000000) dm-5 DellEMC,ME5
size=373G features='0' hwhandler='1 alua' wp=rw
|-+- policy='service-time 0' prio=50 status=active
| |- 11:0:12:2 sdj 8:144 active ready running
| |- 11:0:13:2 sdm 8:192 active ready running
| |- 12:0:12:2 sdv 65:80 active ready running
| `- 12:0:13:2 sdy 65:128 active ready running
`-+- policy='service-time 0' prio=10 status=enabled
|- 11:0:10:2 sdd 8:48 active ready running
|- 11:0:11:2 sdg 8:96 active ready running
|- 12:0:10:2 sdp 8:240 active ready running
`- 12:0:11:2 sds 65:32 active ready running
# blkid | sort -k 2
/dev/mapper/rhel-home: UUID="4ffee200-6075-4bcc-a4b1-a3f76195d310" BLOCK_SIZE="512" TYPE="xfs"
/dev/sda1: UUID="5e59a014-c4c9-42b5-b7f7-f08738843b79" BLOCK_SIZE="512" TYPE="xfs" PARTUUID="38601868-01"
/dev/mapper/mpatha: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdb: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sde: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdh: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdk: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdn: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdq: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdt: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/sdw: UUID="6736b4c1-1fd9-46db-96cb-07b00aa23861" BLOCK_SIZE="4096" TYPE="ext4"
/dev/mapper/rhel-swap: UUID="71dcf2b0-359c-4014-ac99-712ef9b9a952" TYPE="swap"
/dev/mapper/vgapp-lvapp: UUID="77d5cb05-12d0-4005-869a-ba641a6b35ee" BLOCK_SIZE="4096" TYPE="xfs"
/dev/mapper/rhel-root: UUID="9864830b-c4c8-4659-a004-81273adea8fe" BLOCK_SIZE="512" TYPE="xfs"
/dev/mapper/mpathb: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member" (source volume)
/dev/mapper/mpathh: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"(snapshot volume)
/dev/sdc: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdd: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdf: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdg: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdi: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdj: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdl: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdm: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdo: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdp: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdr: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sds: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdu: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdv: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdx: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sdy: UUID="LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur" TYPE="LVM2_member"
/dev/sda2: UUID="PZi6r4-jbnR-RGeH-VY12-HQKS-d1hq-I0S7lL" TYPE="LVM2_member" PARTUUID="38601868-02"
# vgs
WARNING: Not using device /dev/mapper/mpathh for PV LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur.
WARNING: PV LSl9Vy-M3Zi-DrZA-McS1-8O8D-2iQA-CCG8ur prefers device /dev/mapper/mpathb because device is used by LV.
VG #PV #LV #SN Attr VSize VFree
rhel 1 3 0 wz--n- 277.87g 0
vgapp 1 1 0 wz--n- <372.52g 0
# vgimportclone --basevgname vgapp-snapshot /dev/mapper/mpathh
# vgs
VG #PV #LV #SN Attr VSize VFree
rhel 1 3 0 wz--n- 277.87g 0
vgapp 1 1 0 wz--n- <372.52g 0
vgapp-snapshot 1 1 0 wz--n- <372.52g 0
# vgchange -a y vgapp-snapshot
Before modifying the file system UUID
# blkid |grep vgapp
/dev/mapper/vgapp-lvapp: UUID="77d5cb05-12d0-4005-869a-ba641a6b35ee" BLOCK_SIZE="4096" TYPE="xfs" (file system on source volume)
/dev/mapper/vgapp--snapshot-lvapp: UUID="77d5cb05-12d0-4005-869a-ba641a6b35ee" BLOCK_SIZE="4096" TYPE="xfs" (file system on snapshot volume)
Change xfs file system UUID
# xfs_admin -U generate /dev/mapper/vgapp--snapshot-lvapp
Clearing log and setting UUID
writing all SBs
new UUID = 5cdd29ca-0583-4a7d-a85c-3e973939ff3f
Change ext4 file system UUID
# tune2fs -U random {SNAPSHOT VOLUME DEVICE}
Mounting a file system with the same UUID as the source on the same host might result in the following error.
# mount /dev/mapper/vgap--snapshot-lvapp /app-data-snapshot
mount: /app-data-snapshot: wrong fs type, bad option, bad superblock on /dev/mapper/vgapp--snapshot-lvapp, missing codepage or helper program, or other error.
Note: Do not leave the snapshot volume and the source volume attached to the source host permanently. Detach the snapshot volume before rebooting the host. If there is an existing snapshot schedule on the source volume and the number of snapshots has exceeded the retention count defined in the schedule, the snapshot volume might get overwritten by the schedule with the source volume data while it is attached on a host. To prevent the snapshot volume from being overwritten, temporarily expire the schedule by setting the end date/time to the current date/time. Resume the schedule after the recovery operation is complete and the snapshot volume has been detached from the host.