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Adding storage nodes to cluster in alternating site order

Danel_1
Frequent Advisor

Adding storage nodes to cluster in alternating site order

Hi ,

How to create a multi site cluster with 2 sites , 4 nodes ?

how to add the nodes (oreder) to be sure that the data are striped on the primary site , and miroired on the second site.

the goal is to keep the data access with a site down .

Thank

Didier DANEL
7 REPLIES
Patrick Terlisten
Honored Contributor

Re: Adding storage nodes to cluster in alternating site order

Hello,

AFAIK is the order of the nodes the order, in which the nodes are added to the cluster. If you add node 1 and 2 on site A, and node 3 and 4 to site B, the order of the blocks is

Block A site A
Block B site A
Block C site B
Block D site B

The blocks are only copies, AFAIK there is no striping as long as you're suing nRAID 10.

Regards,
Patrick
Best regards,
Patrick
Danel_1
Frequent Advisor

Re: Adding storage nodes to cluster in alternating site order

Yes in fact the volumes will be in netraid10.

can you give me the order with this.

Thank Didier
Patrick Terlisten
Honored Contributor

Re: Adding storage nodes to cluster in alternating site order

Hello,

AFAIK nRAID 10 isn't a mirrored-stripe. It's only copies blocks around the cluster. The order for those copies is the order, in which the nodes are added to the cluster. So in your case I would add first the nodes from you primary site, then the two nodes from you backup side. But AFAIK there is no striping.

Regards,
Patrick
Best regards,
Patrick
Danel_1
Frequent Advisor

Re: Adding storage nodes to cluster in alternating site order

ok thank you ,

I have a another question ?

If i install a multi site cluster with 2 nodes in 2 sites with netraid10 volumes , the data will be mirrored betwen the 2 nodes.
If i extend the configuration to 4 nodes et 2 sites : what about the data ?

in this case i don't loose a site because the data are not copied completely in each site.

What can i do to preserve the role of each site , one primary and one backup ?

regards

Didier



Mark...
Honored Contributor

Re: Adding storage nodes to cluster in alternating site order

Hi
Too try and explain how netraid works:

2 nodes network raid 10 = the same block is written to each node.

4 nodes network raid 10 = the same block is written to two nodes (as before) but the order of the nodes is important. Let us say we have 4 nodes called 1, 2, 3 & 4 and the data blocks we will call A, B, C & D.
This is how the data is written for network raid 10 in a 4 node cluster.

1 = A & D
2 = A & B
3 = B & C
4 = C & D
and so on.

Now if you wish to go multisite you would put nodes 1 & 3 at one site and nodes 2 & 4 at the other site.
Now if you look at the way the data is stripped across the nodes you would see that A, B, C & D data is at both sites.
Hope this helps?
Mark...
if you have nothing useful to say, say nothing...
Danel_1
Frequent Advisor

Re: Adding storage nodes to cluster in alternating site order

Ok , if i understand :

if i install 2 nodes in a multisite cluster
node 1 on site A et node 2 on site B , the data (Netraid10)are on each site.

Next time i extend to 4 nodes node 1 et 3 on site A and 2 and 4 on site B. is the datas stripped on node 1 and 3 and mirrored on nodes 2 and 4 ??

Is a tool available to trace the blocks allocation ?

Regards

Didier
Mark...
Honored Contributor

Re: Adding storage nodes to cluster in alternating site order

Hi,
If there is a tool to track block allocation I have no idea what it is.
To check that the order is correct you need to use the "edit cluster" option from CMC and check the ORDER and LOCATION of the node.
For eaxmaple:

NODE SITE
1 site-a
2 site-b
3 site-a
4 site-b

If it is like the above example then that would be correct - if not then NO!

Mark...
if you have nothing useful to say, say nothing...