Keep the number of disks
in the root volume group to a minimum; HP recommends using three disks,
even if the root volume group is mirrored.
Root volume groups with many disks make reinstallation difficult
because of the complexity of recovering LVM configurations of accessory
disks within the root volume group.
A small root volume group is quickly recovered.
In some cases, you can reinstall a minimal system, restore a backup,
and be back online within three hours of diagnosis and replacement
of hardware. Another benefit is that exact match to the previous root
disk layout is not required.
Three disks in the root volume group are better than
two, because of quorum restrictions. With a two-disk root volume group,
the loss of one disk can require you to override quorum to activate
the volume group; if you must reboot to replace the disk, overriding
quorum requires you to interrupt the boot process. If you have three
disks in the volume group and they are isolated from each other such
that a hardware failure only affects one of them, then failure of
only one disk enables the system to maintain quorum.
There are two reasons to expand the root volume
group beyond a minimal size.
A very small root disk.
In this case,
HP recommends migrating or installing to a larger disk.
Providing for dump-to-swap for large memory systems.
Swap volumes targeted for dump must be in the root volume group.
A better solution is to configure an extra dedicated disk for dump