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

The following output of lvdisplay reflects the changes:

Timestamp Tue Apr 27 13:21:20 2010

Auto Pre-allocation Disabled

Threshold Percent 70

• To enable the automatic increase of pre-allocated extents when lvmpud is not running, enter the

following command:

# lvchange -e y /dev/vgpj/lvol1_S2

The automatic increase of pre-allocated extents has been disabled

since lvmpud is not running. Please start the lvmpud daemon and

enable the feature using lvchange command.

Logical volume "/dev/vgpj/lvol1_S2" has been successfully changed.

Volume Group configuration for /dev/vgpj has been saved in

/etc/lvmconf/vgpj.conf

The automatic increase of pre-allocated extents is enabled only if lvmpud is running.

Changing the attributes of a logical volume having snapshots

You cannot change some attributes of an original logical volume using lvchange if the logical

volume has some snapshot associated with it. The following lvchange options are disabled for this

type of logical volume:

• -s — Sets the strictness policy of the mirrored logical volume.

• -D — Sets the distributed allocation policy.

• -d — Sets the scheduling policy.

• -C — Sets the contiguous allocation policy.

For more information, see lvchange(1M).

HP recommends that the I/O timeout value of a logical volume having snapshots be set to a larger

value to accommodate the CBW I/Os induced by a write I/O to this logical volume. For more

information, see

Changing the attributes of a snapshot logical volume.

Deleting logical volumes on a snapshot tree

To delete snapshot logical volumes from a volume group, use the lvremove command. You can

delete either a single snapshot or a snapshot and all its predecessors using lvremove. Before

removing a logical volume that has snapshots associated with it, you must remove all its snapshot

logical volumes. Ensure that all the snapshots being deleted are closed before issuing the

lvremove command.

When a single snapshot logical volume is deleted, if the snapshot has a predecessor that is not

marked over-committed or inoperative, for all unshare units of the predecessor that share data with

this snapshot, the unshared data of the snapshot is copied to the predecessor. If the predecessor is a

space-efficient snapshot, ensure that sufficient number of extents are pre-allocated to prevent it from

being marked over-committed because of the unshare data copy during snapshot deletion.

For example, you want to delete snapshot S1, and S0 shares data A, C, and D with S1. Of these, S1

shares data A with LV, but has its own copy of C and D, which are referred to as unshared data on

S1. When S1 is deleted, unshare units that contain C and D are copied over to S0, and S0 no longer

shares these units with its new successor LV.