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

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Beginning with the HP-UX 11i v3 September 2010 Update release, LVM provides a feature to
automatically increase the pre-allocated extents when the threshold value is reached. For more
information, see
Enabling the automatic increase of pre-allocated extents.
Enabling the automatic increase of pre-allocated extents
Prior to HP-UX 11i v3 September 2010 Update release, when the number of pre-allocated extents in
the pre-allocated pool falls below the internally maintained threshold value, a message is logged in
syslog and an event is published to the listening subsystems for the user to take action.
Beginning with the HP-UX 11i v3 September 2010 Update release, LVM enables you to automatically
increase the pre-allocated extents when the threshold value is reached and to set the threshold value.
You can enable the automatic increase of pre-allocated extents with the –e option to the lvcreate
or lvchange commands. By default, the automatic increase of pre-allocated extents is enabled.
The lvmpud daemon must be running to enable the automatic increase of pre-allocated extents. For
more information, see lvmpud(1M).
You can change the threshold value using the –P option to lvcreate or lvchange commands.
By default, the threshold is set to the internally maintained threshold value as explained in
Data
Unsharing on Snapshot Logical Volumes. The number of extents that will be incremented automatically
after threshold value is reached is equal to the threshold value.
Note
The lvmpud daemon must be running for this feature to be enabled. Also,
ensure that a sufficient number of extents are present in the volume group
for the automatic increase of pre-allocated extents to succeed.
If the automatic increase of pre-allocated extents is not enabled and the threshold value is set, when
the number of free extents in the pre-allocated extent pool falls below the threshold value, a message
is logged in syslog and an event is published to the listening subsystems for the user to take action.
If neither the -e or -P options are specified, by default, the automatic increase of pre-allocated
extents is enabled and the threshold value is set to the default value.
After the task to automatically increase the pre-allocated extents is posted and it succeeds, LVM prints
the following messages in syslog:
lvmpud->lvextend -l 16 /dev/vg01/lvol1_S2
LVM: The task posted for increasing the pre-allocated extents succeeded
for the snapshot LV (VG 128 0x001000, LV Number: 2).
The lvmpud->lvextend in the preceding message indicates that lvextend was initiated by
lvmpud as a part of automatic increase of pre-allocated extents.
If the task posted to automatically increase the pre-allocated extents fails, the following message is
logged in syslog with appropriate error messages:
LVM: ERROR: The task posted for increasing the pre-allocated extents
failed for the snapshot LV (VG 128 0x001000, LV Number: 2)
If the number of pre-allocated extents incremented automatically is equal to the original logical volume
settings, the following message is logged and no further tasks are posted to lvmpud for further
increase:
LVM: The number of pre-allocated extents for snapshot LV(VG 128
0x001000,LV Number: 2) is equal to the original logical volume's setting.
The number of pre-allocated extents cannot be increased further.