Volume Group Status Area - Structure Definitions.

[sectorseveng]

Does anyone know the structure definitions for the VGSA. ie, location on disk, data type, etc?

I've been able to empirically identify the stale PP map starts at offset 65548, but cannot find any official docs from IBM on the subject.

Any pointers or resources appreciated.

 

[AIXSPadmin]

Just wondering sectorseveng, when you say ..."LVM mirrored VG (where the mirror copy is on a different ESS"...

Surely you are not saying or are mirroring a VG on Shark.

 

[sectorseveng]

AIXSPadmin - Yes, I'm mirroring VGs (parallel schedule) across different Sharks at different locations.
The reasons are:
1. Performance boost on reads. - Either copy can answer
2. Not much performance penalty on writes. - Writing to cache
3. Enhanced availability. - If a shark dies we just carry on running (also useful if we need to take out a shark for maintenance actions).
4. Integration with HACMP. - The PPRC solution is a pig to integrate into site failovers, with LVM mirrors the techniques already exist.

Notes, architecture is HA clusters (each cluster 2 * S80 or S85, 1 way rotating), each servers has 4 FSCSI cards attached to 2 SANs. SAN setup is failsafe but not yet recovery safe (somebody will have to spend more money).

Motto for HA admins "Out, out damned spof!".