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

If a Version 2.2 volume group is deactivated using the vgchange –A n option to skip the

automatic backup of configuration file, this warning is displayed. If the Version 2.2 volume group

contains snapshots, HP recommends that you deactivate the volume group after backing the

configuration file. Do not use the vgchange –A n option if you want to back up the configuration

file before deactivating the volume group.

• 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.

The automatic increase of pre-allocated extents feature cannot be enabled if lvmpud is not running

on the system. Start the lvmpud daemon and then enable the feature.

Performance numbers

With the HP-UX 11i v3 March 2010 Update release, there is no performance degradation for read

and write I/Os on a logical volume that has no snapshots associated with it. Also, when a snapshot is

created, the read I/O performance on the original logical volume does not show any degradation.

Read performance

When snapshots are involved, the performance of read I/Os on the snapshot logical volume has the

following performance degradation:

• Raw random read I/Os on snapshot logical volumes have an average performance degradation of

5%. When the original logical volume and the snapshot are striped, expect up to a 5 to 6%

performance degradation.

• Raw sequential read I/Os on snapshot logical volumes have an average performance degradation

of 15%. When the original logical volume and the snapshot are striped, expect up to a 25%

performance degradation.

• Block random read I/Os on snapshot logical volumes have an average performance degradation

of 1%. When the original logical volume and the snapshot are striped, expect up to a 6%

performance degradation.

• Block sequential read I/Os on snapshot logical volumes have an average performance degradation

of 1%. When the original logical volume and the snapshot are striped, expect up to an 8%

performance degradation.

Note

Over time, as more and more data is unshared between the original logical

volume and its snapshots, the performance degradation of read I/Os

gradually reduces.