Using High Availability Monitors (June 2003)

Monitoring Disk Resources
Rules for Using the HA Disk Monitor with ServiceGuard
Chapter 242
This command creates a 120 MB mirrored volume named lvol1 . The
name is supplied by default, since no name is specified in the command.
The -s g option means that mirroring is PVG-strict, that is, the mirror
copies of data will be in different physical volume groups.
Rules for Mirrored Individual Disks
The following rules apply to configuring mirrored disks for use with
ServiceGuard and the HA Disk Monitor:
• Mirroring must be PVG-strict.
Mirrored volumes must reside on a different bus from the original
volume to avoid a single point of failure and to obtain the best
pv_summary value for that mirror. This is done automatically by LVM
if you have created the PVGs while setting up mirroring. See the
lvextend manpage and Managing MC/ServiceGuard (HP Part
Number B3936-90026) for more information.
• Logical volumes that are 2-way mirrored should be in separate
volume groups from those that are 3-way mirrored.
Putting differently mirrored volumes in the same volume group
makes it difficult to accurately interpret the pv_summary data. Take
the example of a volume group containing both 2- and 3-way
mirroring. If 2 host adapters fail on that volume group, it could mean
no data available for the 2-way mirrored logical volume, but one copy
still available for the 3-way mirrored volume. The pv_summary would
be wrong for one of those mirrored disk configurations.
• Volume groups representing the same hardware for failover must be
created with exactly the same name on all nodes.
For example, a bus connecting 3 nodes to a disk array must be
defined as part of vg01 on all 3 nodes. It is also recommended that
you use the same names for PVGs containing the same actual disks.
Mirrors that have been split off are treated the same by the HA Disk
Monitor as they are by LVM. When you split off a mirror, you will see a
change in the following resources:
• /vg/ vgName /lv/copies/ lvName will be reduced by one when the mirror
is split off. If you have created a monitoring request for that resource
that alerts you when the number of copies is changed or is reduced,
you will see an event.