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8.13. User Serviceable Snapshots
User Serviceable Snapshot is a quick and easy way to access data stored in snapshotted volumes. This feature is based on the core snapshot feature in Red Hat Gluster Storage. With User Serviceable Snapshot feature, you can access the activated snapshots of the snapshot volume.
Consider a scenario where a user wants to access a file
test.txt which was in the Home directory a couple of months earlier and was deleted accidentally. You can now easily go to the virtual .snaps directory that is inside the home directory and recover the test.txt file using the cp command.
Note
- User Serviceable Snapshot is not the recommended option for bulk data access from an earlier snapshot volume. For such scenarios it is recommended to mount the Snapshot volume and then access the data. For more information see, Chapter 8, Managing Snapshots
- Each activated snapshot volume when initialized by User Serviceable Snapshots, consumes some memory. Most of the memory is consumed by various house keeping structures of gfapi and xlators like DHT, AFR, etc. Therefore, the total memory consumption by snapshot depends on the number of bricks as well. Each brick consumes approximately 10MB of space, for example, in a 4x3 replica setup the total memory consumed by snapshot is around 50MB and for a 6x3 setup it is roughly 90MB.Therefore, as the number of active snapshots grow, the total memory footprint of the snapshot daemon (snapd) also grows. Therefore, in a low memory system, the snapshot daemon can get
OOMkilled if there are too many active snapshots
8.13.1. Enabling and Disabling User Serviceable Snapshot
To enable user serviceable snapshot, run the following command:
# gluster volume set VOLNAME features.uss enable
For example:
# gluster volume set test_vol features.uss enable volume set: success
Activate the snapshot to access it via the user serviceable snapshot:
# gluster snapshot activate <snapshot-name>
To disable user serviceable snapshot run the following command:
# gluster volume set VOLNAME features.uss disable
For example:
# gluster volume set test_vol features.uss disable volume set: success
8.13.2. Viewing and Retrieving Snapshots using NFS / FUSE
For every snapshot available for a volume, any user who has access to the volume will have a read-only view of the volume. You can recover the files through these read-only views of the volume from different point in time. Each snapshot of the volume will be available in the
.snaps directory of every directory of the mounted volume.
Note
To access the snapshot you must first mount the volume.
For NFS mount refer Section 6.3.2.2.1, “Manually Mounting Volumes Using Gluster NFS (Deprecated)” for more details. Following command is an example.
# mount -t nfs -o vers=3 server1:/test-vol /mnt/glusterfs
For FUSE mount refer Section 6.2.3.2, “Mounting Volumes Manually” for more details. Following command is an example.
# mount -t glusterfs server1:/test-vol /mnt/glusterfs
The
.snaps directory is a virtual directory which will not be listed by either the ls command, or the ls -a option. The .snaps directory will contain every snapshot taken for that given volume as individual directories. Each of these snapshot entries will in turn contain the data of the particular directory the user is accessing from when the snapshot was taken.
To view or retrieve a file from a snapshot follow these steps:
- Go to the folder where the file was present when the snapshot was taken. For example, if you had a test.txt file in the root directory of the mount that has to be recovered, then go to that directory.
# cd /mnt/glusterfs
Note
Since every directory has a virtual.snapsdirectory, you can enter the.snapsdirectory from here. Since.snapsis a virtual directory,lsandls -acommand will not list the.snapsdirectory. For example:# ls -a ....Bob John test1.txt test2.txt - Go to the
.snapsfolder# cd .snaps
- Run the
lscommand to list all the snapsFor example:# ls -p snapshot_Dec2014/ snapshot_Nov2014/ snapshot_Oct2014/ snapshot_Sept2014/
- Go to the snapshot directory from where the file has to be retrieved.For example:
cd snapshot_Nov2014
# ls -p John/ test1.txt test2.txt - Copy the file/directory to the desired location.
# cp -p test2.txt $HOME
8.13.3. Viewing and Retrieving Snapshots using CIFS for Windows Client
For every snapshot available for a volume, any user who has access to the volume will have a read-only view of the volume. You can recover the files through these read-only views of the volume from different point in time. Each snapshot of the volume will be available in the
.snaps folder of every folder in the root of the CIFS share. The .snaps folder is a hidden folder which will be displayed only when the following option is set to ON on the volume using the following command:
# gluster volume set volname features.show-snapshot-directory on
After the option is set to
ON, every Windows client can access the .snaps folder by following these steps:
- In the
Folderoptions, enable theShow hidden files, folders, and drivesoption. - Go to the root of the CIFS share to view the
.snapsfolder.Note
The.snapsfolder is accessible only in the root of the CIFS share and not in any sub folders. - The list of snapshots are available in the
.snapsfolder. You can now access the required file and retrieve it.
You can also access snapshots on Windows using Samba. For more information see, Section 6.4.8, “Accessing Snapshots in Windows”.
