HP-UX Logical Volume Manager and MirrorDisk/UX Release Notes (March 2010 Update release)

Problem: When the snapshot being deleted has one or more predecessors,
and the operation requires data unsharing, the delete operation can
hang under low memory conditions (This operation requires a
minimum of 8 MB of memory).
Severity: Critical
Corrective Action: If the system hangs, stop other running applications so that enough
memory is available for the lvremove to continue.
TIP: To prevent this error from occurring during the deletion of
a snapshot, ensure the system is not in a low memory condition.
Also, ensure that there are no I/Os in progress on snapshot trees
while the operation is being performed.
Changing timeout for snapshot logical volumes can sometimes hang
Defect ID: QXCR1001002810
Problem: If the timeout value associated with a snapshot or its successor
logical volume is the default and there are I/Os in progress on it or
its successor, changing the timeout value of the snapshot logical
volume can hang if the physical volumes that need to be accessed
to achieve data unsharing for the I/Os are unavailable.
Severity: Medium
Corrective Action: Bring all the physical volumes on which the snapshot extent is
written online.
TIP: Before changing the timeout value for the snapshot logical
volume, ensure that there are no I/Os in progress on it or its
successor logical volumes.
Limitations
This section provides a list of limitations as known to HP at time of publication.
• Logical volumes that have snapshots associated with them might experience an increase in
latencies associated with writes. This is also applicable for writes on (writable) snapshots
themselves.
• When the number of extents remaining in a space-efficient snapshot logical volume’s
pre-allocated pool falls beyond a certain internally computed threshold, a message is logged
in the syslog. This message is displayed to inform you that further unsharing of data
between the snapshot and its successors might end up depleting the extents in the
pre-allocated pool and lead to the snapshot and its predecessors being marked as inoperative.
At this point, you must increase the pre-allocated extent pool size for the snapshot logical
volume.
• Under very low memory conditions, the removal of a single snapshot using lvremove can
hang if data unsharing is required.
• For more limitations on snapshots, see the Using LVM Logical Volume Snapshots white paper.
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