Using High Availability Monitors (June 2003)

Monitoring Disk Resources
Rules for Using the HA Disk Monitor with ServiceGuard
Chapter 238
• n is the number of paths for the volume group in /etc/lvmtab
(physical volumes, paths, or LUNs).
• p is the number of PVGs (physical volume groups) in the volume
group
• x is the number of paths currently available from a SCSI inquiry
To give pv_summary the most accurate picture of data availability, you
need to use PVGs to define your physical volumes as separate access
points to data. Mirroring should be PVG-strict. Arrays should have PV
links, with redundant links in a separate PVG. Note that if you do not
configure PV links into separate PVGs, p in Table 2-7 will always be
equal to 1. Therefore any SCSI inquiry that does not return a value of
UP for every path will result in a calculation of DOWN for pv_summary.
Rules for RAID Arrays
RAID configurations must be configured with PV links. PV links are
redundant links attached to separate controllers on the array. If PV links
are configured, and one fails, LVM automatically switches to the
alternate controller when one fails.
Table 2-7 pv_summary Calculations
Case Conclusion State
x = n All physical volumes and all data
are available.
UP
n>x>=n - (p-1) All data is available. PVG_UP
n / p <= x <= n -( p -1)
If there are PVGs, and one PVG
has all paths, then all data is
available.
PVG_UP
If there are PVGs, and none of the
PVGs has all paths, then the HA
Disk Monitor cannot determine if
all data is available.
SUSPECT
x < n / p Some data is missing.
DOWN
x =0 No data or physical volumes are
available.