SEP sesam uses LVM (Logical Volume Manager) snapshots to perform consistent backups of open files on Linux distributions. LVM snapshots allow to back up a frozen copy of the file system without taking the "live" volume offline during the backup.
A snapshot volume is a special type of volume that temporarily preserves the original data at some point in time and represents an exact copy of a logical volume (LV). It is created as a new logical volume in the same volume group as the original LV. LVM snapshots work only with partitions created with LVM (see prerequisites).
When SEP sesam backs up the LVM snapshot, the data is stored in a saveset using the original pathname. After the backup, SEP sesam performs a cleanup of all LVM snapshots that were created by the same backup job but not deleted (purged) due to errors, etc. You can change this behaviour as described in step 2 below.
To use LVM snapshots for SEP sesam backup, make sure that the following conditions are met depending on the SEP sesam version:
- Installed and configured SEP sesam Server and SEP sesam Linux Client with a partition configured for LVM.
- LVM partition must be added to a volume group (VG) with sufficient free space available for an LVM snapshot.
- SEP sesam ≥ 5.0.0 Jaglion: one or multiple data sources can be selected. Multiple data sources can be:
- different directories on the same LVM partition
- different directories on different LVM partitions on the same volume group (VG)
- different directories on different LVM partitions on different volume groups (VGs)
- SEP sesam ≤ 184.108.40.206 Beefalo V2: data to be backed up with one backup task must be on the same partition. If you want to back up data from more than one partition, you need to set up a backup task for each partition.
Activating LVM backup
For general information on backup configuration and prerequisites, see Standard Backup Procedure. This section covers only LVM-related specifics when configuring a backup task.
In the Main Selection -> Tasks -> By Clients, select your Linux client then click New Backup Task. The New Backup Task window appears. You can create a new backup task or modify an existing one. To specify the Source, click the browse button. Note that the selected data must reside on the same partition. Selecting the source automatically sets the task type and task name.
Select the Backup with LVM option.
- Switch to the Options tab. You can set the following options in the Backup options (previously Save options) field:
The backup will fail if the source path is not on an LVM volume or if VG has no free space.
- snapsize=<size>, where <size> can be specified as:
- 20%ORIGIN; The default snapshot size is 10% of the saved LVM size (10%ORIGIN).
- To allow non-LVM paths to be added as backup sources to the task (with the Backup with LVM option), set this option -a allow_no_lvm=1 In this case, a normal Path backup is created for the non-LVM source.
- By default, SEP sesam automatically deletes the snapshots created by the same backup task after the backup. To delete all SEP sesam snapshots, use the deleteall command: -a snapshot=deleteall If you want to keep the snapshots after the backup is complete, use keepsnap: -a snapshot=keepsnap To prevent the snapshots from being deleted before the backup starts (SEP sesam default behaviour), use the command: -a snapshot=nodeletebefore
- All other options of the -a switch are added to the lv_create call as a long option: -a ignoremonitoring -> lvcreate -s -l 10%ORIGIN -n Sesam_ssid --ignoremonitoring "/dev/sesam/sesam" See Linux man page man lvcreate options -L and -l for supported values.
It is not recommended to use the snapsize option for thin-provisioned volumes as this slows down backup performance. Thus, as of SEP sesam ≥ 5.0.0 Jaglion, this option has no effect on source LVM volumes that are thin-provisioned.