4.5. Creating Snapshot Volumes
4.5. Creating Snapshot Volumes Use the -s argument of the lvcreate command to create a snapshot volume. A snapshot volume is writeable. LVM snapshots are not cluster-aware, so they require exclusive access to a volume. For information on activating logical volumes on individual nodes in a cluster, see Section 4.8, "Activating Logical Volumes on Individual Nodes in a Cluster" . The following command creates a snapshot logical volume that is 100 megabytes in size named /dev/vg00/snap . This creates a snapshot of the origin logical volume named /dev/vg00/lvol1 . If the original logical volume contains a file system, you can mount the snapshot logical volume on an arbitrary directory in order to access the contents of the file system to run a backup while the original file system continues to get updated. After you create a snapshot logical volume, specifying the origin volume on the lvdisplay command yields output that includes a a list of all snapshot logical volumes and their status (active or inactive). The following example shows the status of the logical volume /dev/new_vg/lvol0 , for which a snapshot volume /dev/new_vg/newvgsnap has been created. The lvs command, by default, displays the origin volume and the current percentage of the snapshot volume being used for each snapshot volume. The following example shows the default output for the lvs command for a system that includes the logical volume /dev/new_vg/lvol0 , for which a snapshot volume /dev/new_vg/newvgsnap has been created. Note Because the snapshot increases in size as the origin volume changes, it is important to monitor the percentage of the snapshot volume regularly with the lvs command to be sure it does not fill. A snapshot that is 100% full is lost completely, as a write to unchanged parts of the origin would be unable to succeed without corrupting the snapshot.
lvcreate --size 100M --snapshot --name snap /dev/vg00/lvol1 lvdisplay /dev/new_vg/lvol0 --- Logical volume --- LV Name /dev/new_vg/lvol0 VG Name new_vg LV UUID LBy1Tz-sr23-OjsI-LT03-nHLC-y8XW-EhCl78 LV Write Access read/write LV snapshot status source of /dev/new_vg/newvgsnap1 [active] LV Status available # open 0 LV Size 52.00 MB Current LE 13 Segments 1 Allocation inherit Read ahead sectors 0 Block device 253:2 lvs LV VG Attr LSize Origin Snap% Move Log Copy% lvol0 new_vg owi-a- 52.00M newvgsnap1 new_vg swi-a- 8.00M lvol0 0.20