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

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pvmove , vgmove, and lvmove commands
If a physical volume of a Version 2.2 volume group has pre-allocated extents of a space efficient
snapshot mapped
to it, you cannot use the pvmove automatic rebalance feature on this physical volume. In
this case, use the
pvmove legacy functionality that does not perform the automatic rebalance of extents.
The vgmove operation succeeds even if the physical volumes involved in migration have pre-allocated
extents of a space-efficient snapshot mapped to it.
You cannot use lvmove to migrate extents of a logical volume from one set of physical volumes to
another set of physical volumes belonging to a Version 2.2 volume group if the logical volume is a
space-efficient snapshot and the migration involves moving one or more of its pre-allocated extents.
vgreduce command
You cannot remove a physical volume that has pre-allocated extents from a volume group using the
vgreduce command. For vgreduce to succeed, free up the pre-allocated extents using lvremove
and then run vgreduce.
If you run vgreduce with the -f option on a volume group that has missing physical volumes, and if
any of these physical volumes have pre-allocated extents, vgreduce reports information about these
extents. In this case, free up the pre-allocated extents using lvremove and then re-run vgreduce.
lvsplit and lvmerge commands
You cannot split a mirrored snapshot logical volume, but can split a mirrored original logical volume
with snapshots using lvsplit.
You cannot merge a snapshot logical volume using lvmerge. If either of the logical volume paths
specified to lvmerge is a snapshot logical volume or a logical volume with snapshots, the merge
operation fails.
Although you can split a mirrored original logical volume having snapshots, the split logical volume
cannot be merged back to the original logical volume as long as one of the logical volumes has
snapshots associated with it. To merge the split logical volume back to the original logical volume,
delete the snapshots associated with both the logical volumes (if any) before proceeding with the
merge operation. For more information, see lvsplit(1M) and lvmerge(1M).
vgchange command
Each time the configuration of a volume group changes (with a LVM configuration command), the
configuration backup file is updated automatically, unless disabled by the user explicitly. For a
Version 2.2 volume group with snapshots configured, information related to the data sharing between
a logical volume and
its successor and predecessor is also maintained on disk. This information changes
when a write I/O requires data unsharing. However, this change is not updated in the configuration
file of the volume group for each write I/O. When you use this configuration file to restore to a set of
physical volumes, the data sharing information is stale and can cause data corruption.
To prevent this, vgchange is enhanced to automatically take a backup of the configuration file when
a Version 2.2 volume group is deactivated. If you choose to skip the automatic backup of the
configuration file using the –A n option and use this configuration file to restore all the physical
volumes of the volume group, the correctness of data in the snapshot logical volumes cannot be
guaranteed for the reason mentioned previously. Therefore, HP recommends you not bypass the
update to the configuration file during a volume group deactivation to ensure that the latest data
sharing details are saved in the configuration file.
For more information, see vgchange(1M).