Using EMS HA Monitors

46 Chapter 2
Monitoring Disk Resources
Rules for Using the EMS Disk Monitor with MC/ServiceGuard
Rules for Mirrored Individual Disks
The following rules apply to configuring mirrored disks for use with
MC/ServiceGuard and EMS monitoring:
• 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 created the PVGs while
setting up mirroring. See the lvextend man page and Managing
MC/ServiceGuard 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. We also recommend using the same names for PVGs
containing the same actual disks.
Mirrors that have been split off are treated the same by the disk monitor as they are
by LVM. When you split off a mirror you may 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 created a monitoring request for that resource that alerts you when the
number of copies changes or is reduced, you may see an event.
• /vg/vgName/lv/status will have a new /lvName resource instance that represents
the split off mirror.
• /vg/vgName/lv_summary many change depending on the state of the new logical
volume created by the split mirror.
If you restore the split mirror normally using supported LVM commands, the disk
monitor will detect the merged mirror and reports