Chapter 4. LVM Administration with CLI Commands
36
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.
#
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
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.
#
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
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.
4.6. Controlling LVM Device Scans with Filters
At startup, the
vgscan
command is run to scan the block devices on the system looking for LVM
labels, to determine which of them are physical volumes and to read the metadata and build up a list
of volume groups. The names of the physical volumes are stored in the cache file of each node in the
system,
/etc/lvm/.cache
. Subsequent commands may read that file to avoiding rescanning.
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