NetRAID 4M & MSCS Quorum RAID

[Francesco Tamba]

Hi,

recently HP made an update to their "installation an configuration guide"
for their SCSI controller certified for MSCS, NetRAID 4M.
The first release of this guide was on march 2001 without any remarkable
issue. At the begin of November they made this update:
"HP recommends creating a fault-tolerant RAID type, such as RAID-5 for the
shared quorum drive. RAID-1 mirrors are NOT recommended for the shared
quorum when using the HP NetRAID-4M controller".

Now, is there anybody that also use HP hardware for MSCS and noticed this?
Any comments? I can't see any damn good technical reason for this.

Thanks
Francesco

[Marco Hogeveen]

The reason for this is that there's a very little chance that, in case of hardware failures, the quorum disk splits in halves and each node owns one copy of the quorum.
This could lead to some 'unwanted' results.
Since the possibility that this will happen is so small, RAID1 is still supported, but just not recommended

[Francesco Tamba]

Thanks for your reply but...
How the OS can see a RAID1 logical drive (or Diskset) as two different halves? And in which circumstances (hw failure you said) there is this possibility?
Thanks

[Marco Hogeveen]

When this occurs, the RAID1 splits in halves and each physical disk is owned by one of the nodes.
Therefor, each node thinks it owns the quorum and is the primary node.
I don't exactly know which hardware failures are necessary to get this situation.