HP-UX 11i v3 Using LVM Logical Volume Snapshots (September 2010)

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• The number of extents or size of pre-allocated pool specified in the command is not greater than the
existing value.
• The snapshot logical volume is inoperative.
For example, you have a Version 2.2 volume group vg01 with logical volume /dev/vg01/lvol1
having a space-efficient snapshot /dev/vg01/lvol1_S2. When write I/Os are issued to the
original logical volume, some extents on the space-efficient snapshot get unshared.
# lvdisplay /dev/vg01/lvol1_S2
--- Logical volumes ---
LV Name /dev/vg01/lvol1_S2
VG Name /dev/vg01
LV Permission read-only
LV Status available/syncd, snapshot,space efficient
Snapshot Status operative
Mirror copies 0
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 40
Current LE 10
Allocated PE 3
Stripes 0
Stripe Size (Kbytes) 0
Bad block NONE
Allocation strict
IO Timeout (Seconds) default
Pre-allocated LE 5
Current pre-allocated LE 2
Unshared LE 3
Current pre-allocated PE 2
Original LV /dev/vg01/lvol1
Timestamp Tue Jan 26 16:17:42 2010
At this point, the threshold has not been reached. When more extents get unshared and the threshold
is reached, the following warning is displayed in the syslog:
LVM: WARNING: Snapshot LV (VG 128 0x000000, LV Number: 2) threshold value
reached. Please increase the number of pre-allocated extents for this
snapshot LV
The lvdisplay output shows the number of extents in the pre-allocated pool that were not picked for
any unshare operation in Current pre-allocated LE and the total number of extents that were
pre-allocated to the space-efficient snapshot in Pre-allocated LE. Increase the Pre-allocated
LE value to add more extents in the pre-allocated pool using lvextend.
In this example, when the threshold is reached, lvdisplay shows the following values:
Pre-allocated LE 5
Current pre-allocated LE 1
Unshared LE 4
Use lvextend to add more extents in the pre-allocated pool as follows:
# lvextend -l 8 /dev/vg01/lvol1_S2
Now, lvdisplay shows the following values:
Pre-allocated LE 8
Current pre-allocated LE 4
Unshared LE 4
For more information, see lvextend(1M).