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

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For example, an I/O is issued on the original logical volume of a snapshot tree. The timeout value
for the original I/O is equal to 60 seconds, which means that the I/O is completed (either success
or failure) within 60 seconds. In this case, if the original I/O requires a CBW I/O, the CBW I/O is
also given a timeout value of 60 seconds; the I/O is still completed (either success or failure) within
60 seconds.
If the timeout value set for the original I/O is not enough for the completion of the original I/O and
CBW I/Os induced by it, the original I/O fails with an error indicating that the I/O time budget is
exhausted. Therefore, HP recommends you choose the I/O timeout value of logical volumes on a
snapshot tree that it is comparatively larger (keeping in mind that the original I/O might result in
one or more CBW I/Os) than the I/O timeout value chosen for a logical volume that is not on a
snapshot tree.
• -e — Enables or disables the automatic increase of pre-allocated extents. The default behavior is
to enable the feature. The lvmpud daemon must be running for this feature to be enabled. If not, it
is disabled.
• -P — Sets the percentage threshold value at which increment messages are logged in syslog, or
the automatic increase of preallocated extents is triggered. The value ranges from 1 to 100.
Note
Although the behavior of I/O timeout for logical volumes on snapshot
tree has changed, the behavior and interaction with the I/O timeout for
physical volumes has not changed.
For more information, see lvchange(1M).
Examples
• The output of lvdisplay for space-efficient snapshot /dev/vg01/lvol1_S2 is as follows:
Timestamp Tue Apr 27 13:21:20 2010
Auto Pre-allocation Enabled
Threshold Percent 30
To change the threshold value for /dev/vg01/lvol1_S2 from 30% to 60%, enter the following
command:
# lvchange -P 60 /dev/vg01/lvol1_S2
Logical volume "/dev/vg01/lvol1_S2" has been successfully changed.
Volume Group configuration for /dev/vg01 has been saved in
/etc/lvmconf/vg01.conf
The following output of lvdisplay reflects the change in threshold percent:
Timestamp Tue Apr 27 13:21:20 2010
Auto Pre-allocation Enabled
Threshold Percent 60
• The output of lvdisplay for space-efficient snapshot /dev/vg01/lvol1_S2 is as follows:
Timestamp Tue Apr 27 13:21:20 2010
Auto Pre-allocation Enabled
Threshold Percent 60
To disable the automatic increase of pre-allocated extents and change the threshold percent from
60% to 70%, enter the following command:
# lvchange -e n -P 70 /dev/vg01/lvol1_S2
Logical volume "/dev/vg01/lvol1_S2" has been successfully changed.
Volume Group configuration for /dev/vg01 has been saved in
/etc/lvmconf/vg01.conf