StoreVirtual Calculator

[Tedh256]

oh wow I don't get this at all!

Here is how I think about it:

at the nr10 level each chunk of data is kept twice: call it chunk1a and chunk1b.

Chunk1a is on one node, chunk1b is on another node - that is the nr10 (it is not really traditional raid 10 which is a mirror of mirrors - it is simple raid 1 mirroring, but abstracted to the network-across nodes level).

I do not think striping comes into it at all?

Maybe I am completely lost though - it has happened before!

[oikjn]

If you have only two nodes, it is NR10 is really just NR1, but if you add a third or more node to the system you will get the stripes as well.

For example.  If you have:  Node1 = 100GB, Node2=100GB, Node3=100GB, Node4=100GB and you see the following in CMC:

Cluster-Whateverthenameis

     -Node1

     -Node2

     -Node3

     -Node4

Your available space will show as 400GB for the cluster

If you make a LUN that is NR10 and is 50GB is size, that will consume 100GB of cluster storage, and the data will be stored on all the nodes with Node1's data mirrored on Node2 and Node3's data mirrored on Node4, so if node2 and node4 were to both shut off, your LUN would still be available.

If you do a LUN that is 50GB NR0, that would consume only 50GB space on the cluster and the data would be spread across all four nodes, but if ANY node were to go offline, that LUN would become unavailable.

If you do a LUN that is 50GB NR10+1, that would consume 150GB space on the cluster.  The data layout is a little more complicated with that where I think the data would go 134, 241, 312, 423, but I'm not 100% on that one.

[Tedh256]

I still think something is not right - but short of having time to dig into deep tech detail, I don't know that we can make more certainty here - at least not for myself.

I'll add only that: I believe your nr10 scenario would in fact be 4 copies of each chunk of data, so that a 50GB volume would consume 200GB instead of 100GB of space. I do though agree 100% on your description of nr0 :-)

As I said - I have no confidence that I can describe how it actually works, and while I also don't have confidence that what you describe is actually correct, I find your effort laudable. And perhaps you are correct and I'm just not "getting" it.

I really wish there were better/more detailed descriptions. It's been a couple years since I looked at the documentation, I'll try to do that when I have a few moments.

Thank you again for spending all this time - now, I hope the original poster has had HIS question answered satisfactorily!

[Bart_Heungens]

Hi all,

Like they say, a picture says more than 1000 words...

Hopefully this explains network RAID:

http://www.bitcon.be/networkraid.png

It is explained until 3 copies, I assume you can imagine yourself for 4 copies...

Kr,

Bart

[Tedh256]

lol - ok so no lables. Sigh:

what are the "dynamic pools"? Are these volumes?
The picture seems to show 4 nodes - but what are the B1, B2 items, and why are there 6 of them spread unevenly between the "dynamic pools" and the nodes?

Sorry, I still don't get it. Perhaps I'm dense, but ....

[Bart_Heungens]

Hi,

Don't focus on the Dynamic Pool notation. You can see it as a cluster where you will put your storage nodes in...

B1, B2 and so on are data blocks that you will write from your server onto the nodes. It is just to give you the idea how the data is spread across all nodes.

Yes this is an example of a cluster with 4 nodes, if you would have 6 nodes, data blocks are spread across in the same manner.

The most chosen RAID level is network RAID 10 which is the middle picture. So every block of data (B1, B2 and so on) will be written onto 2 nodes. In the way like it is on the picture.

This is not important if all nodes are in the same server room. However if you want to spread the storage nodes across 2 server rooms, be aware that nodes 1 and 3 should be in 1 server room, and nodes 2 and 4 in the other. Otherwise you would not survive a datacenter failure...

Kr,

Bart

[Tedh256]

AHHHH - excellent, yes!

This is exactly as I thought. There are no stripes, and any one NR10 volume has 2 copies of each chunk of data: 1 copy on 2 different nodes. If I have 2 total nodes in the cluster, or 4 or 6 there are still only 2 copies of each chunk of data, stored on 2 particular nodes.

Thank you ...

[Bart_Heungens]

Correct that is how it works.

You're welcome...

[Tedh256]

so looking back over this monster thread, I can see now that the OP question still has not been answered (sorry if I hijacked your thread!).

I think it is abundantly clear now how to calculate useable storeage when using NR10 volumes and there are 2 nodes:

assuming 1 rg per node, no stand-by drives, then you multiply "right-sized" drive * 7 = total useable storage (this is data drives in one node only, because nr10 is mirroring so the other nodes disks are "lost" to redundancy).

But as you add nodes - you don't lose the same amount of disk space for the 3rd node as you did the 2nd, and I assume that for the 4th node you lose even less, etc .... (again, this is all assuming all volumes are nr10).

So - how do we calculate useable disk space for different cluster sizes?

whew - it took FOREVER to get the question even figured out!!!

lol!

[Bart_Heungens]

Hi,

I don't see the issue, for sure not for NR10, since all the blocks are spread across the nodes... See the picture...

So even if there are 7 nodes with NR10 there are 2 data blocks written for every original data block. So you will loose always 50%... For 2, 3, 4, 5, 6 and so on nodes...

Kr,

Bart