HP StoreVirtual VSA Network RAID question

[Tom Lyczko]

Two servers with HP StoreVirtual VSA are in Network RAID 1, so one gets to use half the actual available storage.

If I add a 3rd server with HP StoreVirtual VSA, that would double the available storage from the first two, correct??

At least that’s how *I* understand how the Network RAID would work…

Thank you, Tom

[Bart_Heungens]

Hi Tom,

Check out my blog on Network RAID...

http://www.bitcon.be/?p=2537

Kr,

Bart

[Tom Lyczko]

@Bart

I wrote Network RAID 1 but I really meant 10 -- whatever is the *default* setting in the VSAs to use.

We have two nodes in NR 10 like you say...on the actual servers the disks are in RAID 5.

If I add a 3rd server (node) I should use which NR -- 10 or 10+1?? (physical server disks would be in RAID 5).

I understood your article in terms of the striping but I want to verify which NR to use when we get to adding a 3rd server node (10?? 10+1??) and then if the three servers have all the same quantity of storage within them that I would effectively have 2/3 of the total storage available to use as active storage for guest VMs??

That's what I can not figure out from your article...what the available storage will be with 3 nodes vs. 2 nodes, my apologies for being so dense...

Thank you, Tom

[Tom Lyczko]

I found a calculator...

http://h20564.www2.hp.com/hpsc/doc/public/display?docId=mmr_kc-0108305

It helped me understand that NR 10 will enable about 50% of raw space to be used, NR 10+2 enables about  25%...

SIGH...

[a_o]

It's not that simple, and it really depends on what you're trying to do.

With 3 Storage nodes, you now have a few more options.:

Say you have 3 nodes each with 10GB. We'll call them nodes A, B & C.

Your raw capacity is 30GB.

First, you must think in terms of LUNs.

For example, if you go with NR10 LUNS, you can create 3 LUNs of 5GB each
LUN1 (5GB  from  Node A, 5GB  from  Node B)

LUN2 (5GB  from  Node B, 5GB  from  Node C )

LUN3 (5GB  from  Node A, 5GB  from  Node C)

As you can see, your useable capacity is always half of raw capacity with NR10.
Also note that with an odd number of nodes, NR10 wil not fully utilize your storage capacity if you have a single LUN.

NR10 is a two node construct. but this is not a real problem, as in real world scenarios you'll probably need multiple LUNs.

However, you may choose NR5 LUNs . Here, you can create 2 Luns of 10GB each
LUN1 (5GB  from  Node A, 5GB  from  Node B, 5GB  from  Node C )

LUN2 (5GB  from  Node A, 5GB  from  Node B, 5GB  from  Node C )

As you can see, with NR5, your useable capacity is always n-1 * raw capacity.

NR5 needs at least 3 nodes.

Note that you can have LUNS of different kinds on the same Management group.

So, for performant LUNs, use NR10, and for archival LUNs, you can use NR5 as they areless performant.

[Bart_Heungens]

I want to add some information on the last comment.

NR10 is not a 2-node construct... It works exactly the same way on a 3, 4, 5 or whatsoever node setup... All blocks are evenly spread accross all nodes.

So in a 3node setup it looks like this:

node 1 : blocks A & C

node 2 : blocks A & B

node 3 : blocks B & C

So every block of data is written on the first available node and the second. Second block goes to second and third node, third block goes to node 3 and 1. And so on...

Calculation of size is fairly simple. Take the amount of all nodes (after the hardware RAID) together and divide it by 2...

Real life example:

3 x 4330 with 8 x 900GB disks.

8 x 900GB is 7,2TB

After hardware RAID5 it means 7 disks x 900GB = 6,3TB

3 nodes makes 18,9TB in the cluster

But with NR10 it makes 18,9 / 2 = 9,4TB

With NR10+1 it would make 6,3TB...

NR10+2 is not possible since there are 3 nodes only (you need 4 for NR10+2) but you have to divide by 4...

Kr,

Bart