Using EMS HA Monitors

42 Chapter 2

Monitoring Disk Resources

Rules for Using the EMS Disk Monitor with MC/ServiceGuard

Table 2-6 is a summary of how pv_summary is calculated where

• 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 and 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 2-6 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.

Table 2-6 pv_summary Calculations

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, LVM

automatically switches to the alternate controller when one fails.

To use the EMS disk monitor with MC/ServiceGuard, PV links must be conﬁgured

in a separate PVGS (physical volume groups). This new requirement allows

pv_summary to accurately calculate data availability based on physical volume

availability, thus including both ACTIVE and INACTIVE volume groups. If PV

Case Conclusion State

x = n All physical volumes and all data are available. UP

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 disk monitor cannot determine if

all data is available.

SUSPECT

x < n/p Missing some data.

DOWN

x=0 No data or physical volumes are available.