Adding to two node cluster

[gkornacki]

I currently have a two node cluster connected via ultra SCSI to two HP disk arrays.

I need to add another node, as cost effectivly as possible.

Is there a something that can go between the nodes and the disk? A multiplexer or some kind of SCSI controler that can handle having three or more nodes plugged in and handle the connection to the disk?

If so could someone point me in the direction of where to get this black box.

Any other solutions?

[Steven E. Protter]

Shalom,

For a three node cluster, I believe you'll need to get a quorum server, because the lock disk mechanism will not work. The Quorum server can be Linux to save money.

The rest is just basic ServiceGuard not a big deal at all.

SEP

[Jeff_Traigle]

Actually quorum servers are only required for 4 or more nodes. Besides, the basic issue of all nodes requiring access to the shared data still exists regardless of the locking mechanism used.

It's possible to connect systems and arrays into a SCSI chain using some splitter adapters to connect two SCSI cables to a single SCSI device or HBA. This also requires changing the SCSI ID on some of the HBAs or you'll end up with conflicts for ID 7. It's not pretty and probably not officially supported, but it works and the only additional cost is for the splitters.

[gkornacki]

Thanks. I'm aware of the SCSI bastardization method and don't want to go that route, this is a production system that needs to be up 24x7. I am more felxible with the cost if there is a peice of hardware. There has to be a peice of hardware I'm looking for.

I think it would be easier to build a whole new cluster with new HW and new SW releases. If the pockets were only deeper.

[Ian Vaughan]

Howdy,
What are the HP disk arrays that you currently have?
Why the requirement for a third node - is it an application layer - does it really need to be in the cluster - does it need to be HP-UX?

Does it not make more sense to go fibre channel and walk away from SCSI? Will something like a pair of MSA1000's have enough grunt to provide what you are after?
You would only need a sprinkling of A6795A HBA's and you would be off and running.

A remarketed MSA1500 or MSA1000 pair with all the bells and whistles would only put a small dent in your budget and would be much more reliable than a home brew SCSI lash-up.
Hope this helps.
Ian

[Stephen Doud · Accepted solution]

HP supports only configurations it has tested for durability.

HP no longer supports a SCSI disk-based cluster of more than 2 nodes.

Each SCSI controller must have a unique SCSI address. On legacy products, a switch bank on the adapter had to be configured to a unique address, however for the latest server models, the SCSI address of an adapter can be changed at the boot-time prompt (such as BCH) of the server.

HP used to recommend inline-SCSI-bus-terminated cables to allow a server to be powered down without causing the bus transmission to fail, but such is not the case anymore.