How cephfs snapshots works

This document (000019627) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Enterprise Storage 6

Situation

Customer needs to implement cephfs snapshots and basic understanding of snapshots.

Resolution

How cephfs snapshots works:

cephfs snapshots are managed in the ".snap" subdirectory.

Snapshots can be created/deleted as often as desired. (Hourly, Daily, Weekly, etc...)

Example how to create cephfs snapshots:

Note: Each snapshot is a read only view of the parent directory at the time the snapshot directory was created:

Create file “test-1” and “snapshot01”:

cephfs-client:/mnt/cephfs/compression # ll

total 0

cephfs-client:/mnt/cephfs/compression # touch test01

cephfs-client:/mnt/cephfs/compression # cd .snap

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot01

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot01/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

Create file “test-2” and “snapshot02”:

cephfs-client:/mnt/cephfs/compression # touch test02

cephfs-client:/mnt/cephfs/compression # ll

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot02

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot02/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot01/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

Create file “test-3” and “snapshot03”:

cephfs-client:/mnt/cephfs/compression # touch test03

cephfs-client:/mnt/cephfs/compression # ll

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot03

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot03/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot02/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot01/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

Example how to recover data from snapshots:

Now deleting “test01” and creating "snapshot04":

cephfs-client:/mnt/cephfs/compression # rm test01

cephfs-client:/mnt/cephfs/compression # ll

total 0

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot04

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot04/

total 0

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

Note: “test01 was deleted, but still exists in each of the older snapshots.

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot03/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot02/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

cephfs-client:/mnt/cephfs/compression/.snap # ll snapshot01/

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

Recover “test01” from the most resent snapshot. I would assume that this would be the most typical use case, but the could be reasons for choosing the file from a previous snapshot as well.

cephfs-client:/mnt/cephfs/compression/.snap/snapshot03 # ll

total 0

-rw-r--r-- 1 root root 0 May 15 09:19 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap/snapshot03 # cp test01 /mnt/cephfs/compression/

Note: “test01” was recovered from the snapshot.

cephfs-client:/mnt/cephfs/compression # ll

total 0

-rw-r--r-- 1 root root 0 May 15 09:27 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

Snapshotting will use extra disk space as it keep versions of the files:

Example: Add data to “test01”

cephfs-client:/mnt/cephfs/compression # echo "this is a test" > test01

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot05

cephfs-client:/mnt/cephfs/compression/.snap # cd snapshot05

cephfs-client:/mnt/cephfs/compression/.snap/snapshot05 # ll

total 1

-rw-r--r-- 1 root root 15 May 15 09:42 test01

-rw-r--r-- 1 root root 0 May 15 09:20 test02

-rw-r--r-- 1 root root 0 May 15 09:22 test03

cephfs-client:/mnt/cephfs/compression/.snap/snapshot05 # cat test01

this is a test

Now add more data to “test01” and create "snapshot06"

cephfs-client:/mnt/cephfs/compression # echo "this is another test" >> test01

cephfs-client:/mnt/cephfs/compression # cat test01

this is a test

this is another test

Note: Each snapshot has its own version of “tes01” with it unique content.

cephfs-client:/mnt/cephfs/compression/.snap # mkdir snapshot06

cephfs-client:/mnt/cephfs/compression/.snap # cd snapshot06

cephfs-client:/mnt/cephfs/compression/.snap/snapshot06 # cat test01

this is a test

this is another test

cephfs-client:/mnt/cephfs/compression/.snap # cd snapshot05

cephfs-client:/mnt/cephfs/compression/.snap/snapshot05 # cat test01

this is a test

How to delete a snapshot:

cephfs-client:/mnt/cephfs/compression/.snap # ll

total 0

drwxr-xr-x 2 root root 1 May 15 09:19 snapshot01

drwxr-xr-x 2 root root 2 May 15 09:20 snapshot02

drwxr-xr-x 2 root root 3 May 15 09:22 snapshot03

drwxr-xr-x 2 root root 2 May 15 09:24 snapshot04

drwxr-xr-x 2 root root 3 May 15 09:27 snapshot05

drwxr-xr-x 2 root root 3 May 15 09:27 snapshot06

cephfs-client:/mnt/cephfs/compression/.snap # rmdir snapshot01

cephfs-client:/mnt/cephfs/compression/.snap # ll

total 0

drwxr-xr-x 2 root root 2 May 15 09:20 snapshot02

drwxr-xr-x 2 root root 3 May 15 09:22 snapshot03

drwxr-xr-x 2 root root 2 May 15 09:24 snapshot04

drwxr-xr-x 2 root root 3 May 15 09:27 snapshot05

drwxr-xr-x 2 root root 3 May 15 09:27 snapshot06

Status

Top Issue

Additional Information

Also see:
Managing CephFS Snapshots in the SES6 Administration Guide:
https://documentation.suse.com/ses/6/single-html/ses-admin/#cephfs-snapshots

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.