HP-UX Logical Volume Manager and MirrorDisk/UX Release Notes HP-UX 11i v3 September 2013 Web Release B.11.31 (5900-3304)

4.2 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.
• With the automatic extent pre-allocation feature available in the HPUX 11iv3 September 2010
update and later releases, when the number of extents remaining in a space-efficient snapshot
logical volume’s pre-allocated pool falls beyond a certain internally computed threshold, by
default, LVM tries to increase the pre-allocated pool size by threshold value. This does not
guarantee that snapshot will not become over-commit. For example, if the I/O rate is faster
than auto pre-allocation, the snapshot becomes over-commit.
If auto pre-allocation is manually disabled, 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. As soon as you see this message in the syslog,
you must increase the pre-allocated extent pool size for the snapshot logical volume.
• Automatic increase of pre-allocated extents does not prevent snapshots from becoming
inoperative. If the I/O rate is faster than pre-allocation, it is possible that the free extents are
picked before pre-allocation happens and the subsequent I/O marks the snapshot as
inoperative.
• 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.
5 Installation requirements
This section describes the installation requirements for this release.
5.1 Required hardware
LVM and MirrorDisk/UX have no additional hardware requirements other than the requirements
of the HP-UX 11i v3 operating system. Both products run on all supported HP 9000 and HP Integrity
servers. However, there are specific hardware (HBAs) prerequisites for using LVM boot disks of
size greater than 2TB. For information about hardware supported with LVM boot disks of size
greater than 2TB, see the LVM System Administration Guide at http://www.hp.com/go/
hpux-LVM-VxVM-docs .
5.2 Required software
Because LVM is installed with the HP-UX 11i v3 operating environment, there are no additional
software requirements other than the requirements of the HP-UX 11i v3 operating system.
MirrorDisk/UX requires the BaseLVM™ product.
5.3 Required patches
In HP-UX 11i v3, LVM and MirrorDisk/UX do not require any software patches unless LVM boot
disk of size greater than 2TB is used. Other HP-UX subsystems, however, have released patches
to address issues related to LVM. For each of the following subsystems, you can download patches
from the following website:
http://www2.itrc.hp.com/service/patch/mainPage.do
8 Logical Volume Manager and MirrorDisk/UX Release Notes