StoreVirtual Calculator

[cursur949]

I am currently trying to figure out the math behind calculating storage capacities for the new StoreVirtual line, I know there is a calculator out there for the P4000 series gear but it does not have the 4330 part numbers loaded up yet and I kind of just want to understand it so I it is being done right.

Basically what I am trying to do is calculate how much usable storage I would have if I had two B7E17A or three B7E17A or fore B7E17A

B7E17A = 4330 w/8 450GB drives

Thanks in advanced for your help

[oikjn]

depends on your hardware raid level you want to run and your network raid level you want to run.  Typically its raid5 with two raid groups per shelf and network raid10.

If you can't calculate the raid5 space, its the # of hdds in the group minus one and then multiplied by the HDD capacity.  Network raid works just like regular raid for space, so NR10 gives you 1/2 the available space you have left after the raid5 groups are combined.

I like http://www.ibeast.com/content/tools/RaidCalc/RaidCalc.asp as a raid calculator, but it doesn't do raid6.

Assuming hardware raid5 w/ 4 per group(including a hot spare per group), you would get 838GB usable storage per node assuming NR10 and you have two or more nodes.  If you do one large raid5 group, you would get 1257GB, but you would have a 8 drive group(including one spare) raid5 which might be a bit long for rebuild on a drive failure.  You could also get 1047GB out of a raid6 group with one spare.

Any way you look at it, its always sad when you think about how much usable space you actually have after you take into account hardware and network raid.  That said... such is the cost of the kind of availability you get from network raid...  raw capacity is relitively cheap... availability is not.

[cursur949]

Oikjn and all –

Thanks for responding. My question is less about how raid works and network raid works but more about the actual math works as I am extremely familiar with how raid works. More specific questions below –

How does the network raid math work when adding a third node to a two node cluster? The confusion here come from if you have two drive raid you are technically using raid 1 if you have a three drive raid you are using raid 5 so the same thing should apply for network raid. In this example the raid 1 I would lose the capacity of 50% of the nodes (after hardware raid) and with raid I would lose the capacity of 1 total drives (or one node)

How does HP calculate usable drive capacity after right loss?

The way I think the equation should work out is below though I am not sure if I am right.

Drive size = DS

Write loss = WL (not sure how to calculate this)

Total number of drive in an node = ND

Raid loss = RL (this assumes you know how to calculate hardware raid loss)

Total node capacity of a node = TNC

Total Cluster Nodes = TCN

Total usable capacity = TUC

(DS-WL)*(ND-RL)= (TNC)

Then to calculate the total usable storage of a two node cluster

TNC/TCN=TUC

Then to calculate the total storage of a three node cluster

TNC/???=TUC

[oikjn]

I'm a little lost there.   If you know how hardware raid works, you should know how to calculate your usable space.

I can't remember the formula for conversion from HDD manufacturer's capacity claims to usable space, but that link I gave has it built in.  For 450GB hdd you get 420GB usable per drive.  The usable space for the raid is dependent on the raid level you select, but don't forget about making sure you have hot-spares in your setup (I guess you could make the decision that you would rather get the capacity and are ok that if a drive fails you have lost your hardware redundancy and would rely on your network redundancy for availability until a new drive is shipped in).  The max node capacity you could get would be an 8 drive raid5 group which gives you 2933GB usable space per node with no hot-spare according to the raid calc link I gave.  If you do NR10, that would give you 1466GB usable space on the san per node.

Assuming you use NR10 and all nodes are equal capacity, the total capacity of your san would be the sum of the total usable capacity of each node divided by TWO... this works even for odd numbers of nodes.

[Tedh256]

Network raid 10 is network raid 10 - whether you have 2 nodes or 5 or 7 or 8

Basically SanIQ ensures that there are 2 of each chunk of data, spread across the nodes. (I don't think that it puts chunks of any particular volume on more than 2 nodes - but it always ensures that there are 2 chunks and that each chunk is on a different node)

I wish there were more clearly articulated documentation about exactly how it works - but for sizing questions it is:

right-sized drive size * number of drives - number of drives used for parity / 2

[oikjn]

I believe the manual does spell out exactly the pattern that NR10 gives you.  I know for an even number of nodes, (and assuming you label your nodes 1,2,3,4 and they are ordered in CMC that same way), the data is mirrored between the mirror is every other node and the stripe is the adjacent node, so 1+3 are mirrors and 1+2 are stripes.

For NR10 the data has exactly two copies of the data, if you do NR10+1, the data has three copies, NR10+2 has four.

[Tedh256]

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@oikjn wrote:

the data is mirrored between the mirror is every other node and the stripe is the adjacent node, so 1+3 are mirrors and 1+2 are stripes.

I'm not sure what you mean by "1+2 are stripes"? Could you try to elaborate? I usually think of a "strip set" as being essentially the opposite of mirroring: where a "volume" is striped across 2 (or more) physical devices with no parity or mirroring, so that if one of the devices fails, the whole "stripe set" or volume fails.

I don't think that SanIQ does that when using nr10 does it? Or what am I missing?

[oikjn]

good call.  Sorry about that.  Mental fart.  every time I said stripe I meant mirror.

NR10 has two copies of the same data

NR10+1 has three copies fo the same data

NR10+2 has four copies of the same data.

[Tedh256]

So instead of " so 1+3 are mirrors and 1+2 are stripes" you meant:

 so 1+3 are mirrors and 2+4 are mirrors. I *think*

;-)

[oikjn]

damm I confused things up with my words :)

1+3 are stripes and 1+2 are mirros.  1+3 are the Raid0 part and 1+2 are the Raid1 part..  If node one goes down, your LUN availability will be dependent on node two staying available.