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Adding Storage to Cluster

DKHenery
Occasional Visitor

Adding Storage to Cluster

We currently have 4X 4530 Storevirtual SANs in a Cluster and have some Volumes using 4Way Mirroring.  All 4 nodes have MDL SAS 7.2K drives. We want to add 2X 4530s with 10K SAS Drives for Data Tiering and Adaptive Optimization. I know there will be restriping across the cluster for this, but how or will the 4Way Mirrors be affected since there wil now be 6 Nodes in the cluster?

2 REPLIES
Bart_Heungens
Honored Contributor

Re: Adding Storage to Cluster

It is not possible to do tiering by adding SAS nodes in a cluster with MDL SAS drives. AO is there only with the 4335 nodes with tiering to SSD.

What will happen now is that the first block of data will be on node 1, 2, 3 and 4, the second blovk of data on nodes 2, 3, 4 and 5, third block of data on nodes 3, 4, 5 and 6, and so on... So yyes you can have 4way mirror on 6 nodes, but you will have the performance of MDL SAS drives...

As well be sure that the 10K SAS drives have the same size (or bigger) as the MDL SAS drives... If not your cluster size will shrink!

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oikjn
Honored Contributor

Re: Adding Storage to Cluster

don't do it.

your cluster speed and capacity is based off of the slowest node and the smallest capacity so it is important to make sure you don't make a large mix of different type nodes within a single cluster.  mixing 7.2 and 10k drives will mean that you will only get the speed equivalent of 7.2k out of your 10k nodes.  Additionally, I don't know the capacity of the new and old nodes you mention, but if the 10k nodes are smaller in size, you may end up LOSING cluster total capacity instead of gaining capacity as the usable space on each node is only equal to the usable space on the smallest node.  For example, if you have 3x 50gig nodes and add 3x 20gig nodes to it, your total cluster usable capacity will go from 150gig to 120gig even though you went from 3x nodes to 6x nodes! 

 

Finally... why are you doing a 4-way mirror?  that is pretty rare unless you are on a multi-site cluster and want single node failover redundancy at each site.  Typically 2-way mirror is all that is needed.  The mirroring is done at the cluster block level and not at the node level, so as long as you meet the minimum node requriements to enable that protection level you can enable it, so for 2-way mirror (NR-10) you need >=2 nodes, for 4-way mirror (NR-10+2), you need 4-nodes, but it is valid to have 3-nodes or more with 2-way mirror and 5+ for 4-way.  Also...  the protection level is actually at the LUN level so if most of your data is OK to have in 2-way mirror, you can do that for most data and then have the ultra-critical data in 4-way mirror. 

 

Best bet for the new nodes (unless their size is slightly larger than the original nodes) is to create a new cluster to hold those two nodes (also assuming your data is OK in NR-10 and not NR-10+2).