Lustre 1.6 Operations Manual

15.3 LVM Snapshots on Lustre Target Disks
Another disk-based backup option is to leverage the Linux LVM snapshot
mechanism to maintain multiple incremental backups of a Lustre filesystem. But
LVM snapshots cost CPU cycles as new files are written, so taking snapshots of the
main Lustre filesystem will probably result in unacceptable performance losses.
To get around this problem, create a new, backup filesystem and periodically back
up new/changed files. Take periodic snapshots of this backup filesystem to create a
series of compact "full" backups.
15.3.1 Creating LVM-based Lustre Filesystem As a
Backup
To create an LVM-based backup Lustre filesystem.
1. Create LVM volumes for the MDT and OSTs.
First, create LVM devices for your MDT and OST targets. Do not use the entire
disk for the targets, as some space is required for the snapshots. The snapshots
size start out as 0, but they increase in size as you make changes to the backup
filesystem. In general, if you expect to change 20% of your filesystem between
backups, then the most recent snapshot will be 20% of your target size, the next
older one will be 40%, and so on.
cfs21:~# pvcreate /dev/sda1
Physical volume "/dev/sda1" successfully created
cfs21:~# vgcreate volgroup /dev/sda1
Volume group "volgroup" successfully created
cfs21:~# lvcreate -L200M -nMDT volgroup
Logical volume "MDT" created
cfs21:~# lvcreate -L200M -nOST0 volgroup
Logical volume "OST0" created
cfs21:~# lvscan
ACTIVE
'/dev/volgroup/MDT' [200.00 MB] inherit
ACTIVE
'/dev/volgroup/OST0' [200.00 MB] inherit
15-6 Lustre 1.6 Operations Manual • September 2008