Network RAID10 - 2 node vs. 4 node?

[Paul Hutchings]

In a two-site multi-site SAN, what are the benefits of having a single 4 node cluster vs. 2 x 2 node clusters if all volumes are going to be Network RAID10 please?

The guests/initiators would be linux so there's no DSM MPIO and performance is the requirement over capacity.

Thanks,
Paul

[kghammond]

I can give you one big benefit of having four nodes over two sets of two nodes. If you take one node down, you only lose 25% of your IOPS. If you go with the two sets of two nodes, when you take one node offline, you will lose 50% of your performance on that cluster instead of 25% of the performance of the cluster.

We have noticed VMware get very sluggish when we take one of our nodes offline on our two node clusters when they are heavily used.

When we take a node offline on our four node clusters, no one can tell it is offline.

[Bart_Heungens]

It depends also if you want/can use your ISL intersite-link only for replication trafic or also for active iSCSI sessions from all hosts... If bandwidth and latency permits go for the 4node setup, if ISL is a constraint go for the 2node solution...

[Jitun]

With a 4 Node Multisite setup, you have your data on both the sites.
Hence an acknowledgement needs to travel to and fro between the sites which in most cases is always higher than within the site.

This adds an additional latency.

So I would suggest 2 node 2 clusters for performance.

[aqualityplace]

Check latency between the sites, if its >1ms go for a 4 node multi-site cluster. Hosts will read from the "local" nodes.

I think HP recommend up to 4ms, buit this may slow down application response for writes.