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

marked as inoperative because the data unshare operation fails to complete. After a snapshot is

marked inoperative, all its predecessors that share data with this snapshot are also marked as

inoperative. A fully-allocated snapshot can never become over-committed because all snapshot extents

are allocated at the time of snapshot creation. Figure 3 shows the different snapshot states.

Figure 3: Snapshot state diagram

Operative

Over-commit,

Inoperative

Failed to find an appropriate

extent in the pre-allocated

pool. (space-efficient

snapshots only)

• I/O or data unshare on

the snapshot failed.

• If the snapshot shares data

with its successor and the

successor is marked as

inoperative.

To prevent a space-efficient snapshot from becoming over-committed, LVM internally maintains a

threshold value for the number of extents in the pre-allocated pool. The threshold value is computed

based on one of following allocation policies:

• Non-contiguous allocation policy

The threshold is reached when the number of free extents in the pre-allocated pool is less than or

equal to 20 percent of the total number of extents in the pre-allocated pool.

• Striped allocation policy

The threshold is reached when the free extents in the pre-allocated pool form less than 2 full

extent stripes. With HP-UX 11i v3 October 2010 web release, the threshold is reached when the

number of full extent stripes that can be formed using free pre-allocated extents is less than or

equal to 20 percent of the total pre-allocated extents rounded up to the stripe width divided by

the stripe width.

• Distributed allocation policy

The threshold is reached when the number of free extents in the pre-allocated pool is less than or

equal to 20 percent of the total number of extents in the pre-allocated pool or when more than half

of the number of free extents in the pre-allocated pool is from the same physical volume.

Note

Contiguous allocation policy is not supported for a space-efficient snapshot.

When the number of extents in the pre-allocated pool reaches the threshold value, LVM prints the

following message in the syslog: