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Network RAID10 with 3 nodes?

Paul Hutchings
Super Advisor

Network RAID10 with 3 nodes?

Daft question perhaps, but if you have three sites and create a volume that is Network RAID10, what dictates which nodes get the blocks and how many sites you can lose before you lose access to those volumes please?

 

Thanks.

5 REPLIES
oikjn
Honored Contributor

Re: Network RAID10 with 3 nodes?

daft indeed.

 

 

just joking.  in the cope of things, that one isn't really too bad.

 

 

I assume you didn't mean sites, but nodes.  Network raid10 provides a single node redundancy.  The data is split across the nodes evenly so you have data on (node1 and node2) or (node1 and node3) or (node2 and node3).  You can lose any one node and not have data loss.

 

I THINK, but it isn't documented, that the stripe order is from top down on the cluster, but I don't think it matters too much for raid10.   If you are actually talking about sites and not nodes, then this is a different story unless your sites only have one node.  If you actually are talking about sites with multiple nodes on a site, then it does raid0 at each site and raid10 across the sites...  at least that is what it did for me when I had two sites with two nodes each.  I could change how the stripe ran by changing the order of the nodes in the cluster on the CMC where it would span the even nodes and strip the odds.  I didn't try three sides, but I think raid10 will only allow for one logical group failure, if you want to be able to lose two, you need raid10+1

 

Paul Hutchings
Super Advisor

Re: Network RAID10 with 3 nodes?

I've asked worse :)

 

I do mean sites.  Right now we have a two site multi-site cluster.

 

I'm interested what options I'd have with a three site cluster if I didn't want to use Network RAID5 due to the performance impact (which I must admit I've not tried, but everything I hear suggests there is one so hardware RAID5 + Network RAID5 = evil!).

oikjn
Honored Contributor

Re: Network RAID10 with 3 nodes?

what kind of redundancy are you looking for?  Other than raid10+1, I can't think of a real good reason to do a three site cluster since no matter how you split it, you will have to have 1/3 of your data located only on the two remote sites.  Not that this could stop the cluster from working, just that it would mean that your latency on 1/3 of your load would be higher since it is 100% off-site.

 

Obviously, if you are only trying to increase your storage space, raid10+1 is out of the question, so you have to ask yourself if you are trying to add this extra site to add more storage or add more redundancy... Unfortunately you can't do both by simply adding an extra identical site.

Paul Hutchings
Super Advisor

Re: Network RAID10 with 3 nodes?

At this point being able to lose one site is good.  Being able to lose 2 is better, but right now I'm exploring options - there's no specific need we have that two sites wouldn't address - basically the joys of a big campus, lots of fibre, and lots of VSA licenses :)

 

I'd be interested to know if anyone has used RAID 10+1 and how big the impact was over RAID10

oikjn
Honored Contributor

Re: Network RAID10 with 3 nodes?

I do love the 10-pack VSAs.  When you have them and you have the extra hardware they are a dream.

 

I haven't run raid10+1 at any real scale (just a six-node raid10+1), but I didn't notice any performance cost when everything was kept on the same campus....  the only potential tough deal is that all of your disks need to be about the same capacity (both IO and storage).  The cluster is only as quick as the slowest node, so if you are thinking about throwing in even one weaker node into the same cluster, you are better off making that third site as a remote replication partner than part of the production cluster.