HP HA s Software manual Rules for RAID Arrays, Pvsummary Calculations Case Conclusion State

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
		Case	Conclusion	State
	x = n		All physical volumes and all data are available.	UP
	x=n-(p-1)		All data is available.	PVG_UP
			If there are PVGs, and one PVG has all paths,	PVG_UP
	n/p <= x <= n-(p-1)		then all data is available.
			If there are PVGs, and none of the PVGs has all	SUSPECT
			paths, then the disk monitor cannot determine if
			all data is available.
	x < n/p		Missing some data.
				DOWN
	x=0		No data or physical volumes are available.

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

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