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

14
Mirror copies 0
Consistency Recovery MWC
Schedule parallel
LV Size (Mbytes) 400
Current LE 200
Allocated PE 30
Stripes 0
Stripe Size (Kbytes) 0
Bad block NONE
Allocation strict
IO Timeout (Seconds) default
Pre-allocated LE 170
Current pre-allocated LE 140
Unshared LE 30
Current pre-allocated PE 140
Original LV /dev/vg01/lvol1
Timestamp Wed Apr 28 14:01:14 2010
Auto Pre-allocation Enabled
Threshold Percent 70
The next time, the threshold value is calculated as 70% of 170 extents. By increasing the
pre-allocated pool size by 70%, the size of the snapshot crosses the original logical volume size.
Therefore, it is increased to maximum size of original logical volume.
For more information on using this feature, see lvmpud(1M), lvcreate(1M), lvchange(1M),
and lvm(7).
Changing the Attributes of a Snapshot Logical Volume
You can change only some attributes of a snapshot logical volume. Use the following lvchange
options to change attributes of the snapshot logical volume. The options and their values remain the
same as they are for normal logical volumes. For more information, see lvchange(1M).
• -p — Sets the access permission of the snapshot logical volume. By default, the snapshot is read-
only. Use this option to make the snapshot writable.
• -M and –c — Sets the mirror consistency recovery policy.
• -a — Changes the availability of the snapshot logical volume. If the snapshot logical volume is
made unavailable using this option, I/Os are not allowed to succeed. However, you can still
unshare data on this snapshot logical volume because of write I/Os on its successor. In case of
space efficient snapshot logical volumes, if enough extents are not available for unsharing, it might
become over-committed and inoperative. If the space-efficient snapshot was made temporarily
unavailable but its data is still useful, HP recommends that you monitor the space efficient snapshot
for the threshold value of number of extents in its pre-allocated pool. When the threshold is
reached, increase the number of extents in the pre-allocated pool using lvextend or enable the
feature to automatically increase the pre-allocated extents. For more information, see
Extending the
pre-allocated extent pool and Enabling the automatic increase of pre-allocated extents, respectively.
• -t — Changes the I/O timeout value for the snapshot logical volume. An I/O issued on any
logical volume on the snapshot tree might result in one or more CBW I/Os as a part of data
unsharing process. The timeout value for each CBW I/O is inherited from the original I/O that
induced it. However, the time budget for completion of the whole I/O (including the original I/O
and its CBW I/Os) is still equal to the I/O timeout value of the original I/O and not the sum of the
original I/O timeout and CBW I/O timeout values. Also, LVM I/O retry policy based on the I/O
timeout value in case of I/O failure still remains the same for the I/O on a logical volume on the
snapshot tree, as with any I/O on a logical volume not on a snapshot tree.