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Maximum cluster nodes in SQL AlwaysOn Expand / Collapse
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Posted Monday, March 17, 2014 1:35 PM
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Hi,

How many nodes can you have in a cluster with SQL 2012 alwaysOn.
I understand that availability groups are limited to 5 nodes but if you had a 10 node cluster and decided to create multiple availability groups using various nodes within the 10 nodes but never exceeding 5, is that possible?
Or is there a counter or some validation from SQL AlwaysOn that actually hard limits to a grand total of 5 nodes in a cluster?

Cheers
Post #1551887
Posted Monday, March 17, 2014 3:08 PM
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Yeah, That's the limitation imposed by the architecture of Always ON itself. So even though you have 10 nodes, each AG can have 1 Primary replica and upto 4 Secondary replicas. If you try to add a 5th secondary replica you will get an error.

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Post #1551928
Posted Monday, March 17, 2014 3:21 PM
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Thanks for reply, i understand that part, but what if you have this example.

10 node windows cluster
Availability group 1 spans nodes 1 -5.
Availability group 2 spans nodes 5-10.

Essentially you have a massive windows cluster with pockets of availability groups defined throughout.

Post #1551932
Posted Monday, March 17, 2014 3:48 PM
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glugingboulder (3/17/2014)
Thanks for reply, i understand that part, but what if you have this example.

10 node windows cluster
Availability group 1 spans nodes 1 -5.
Availability group 2 spans nodes 5-10.

Essentially you have a massive windows cluster with pockets of availability groups defined throughout.



I didn't test it but I think that should be fine. The actual requirement is the availability replica should be part of the instances on the nodes of same WSFC.

AG1 and AG2 should have different set of databases.

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Post #1551949
Posted Monday, March 17, 2014 7:26 PM
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Yeah i'm thinking it would be fine, haven't tested either.
I believe Vmware ESX 5.5 supports a maximum of 5 nodes in a windows cluster, that's what made me think possibly there was a limitation on total cluster size in SQL AlwaysOn.

Cheers

Post #1551973
Posted Tuesday, March 18, 2014 11:27 AM
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glugingboulder (3/17/2014)
Yeah i'm thinking it would be fine, haven't tested either.
I believe Vmware ESX 5.5 supports a maximum of 5 nodes in a windows cluster, that's what made me think possibly there was a limitation on total cluster size in SQL AlwaysOn.

Cheers



Yeah, Window 2008 R2 and above supports upto 5 nodes for ESX 5.5. Always ON doesn't impose the node limitation.
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Post #1552336
Posted Wednesday, March 19, 2014 5:15 AM


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glugingboulder (3/17/2014)
Thanks for reply, i understand that part, but what if you have this example.

10 node windows cluster
Availability group 1 spans nodes 1 -5.
Availability group 2 spans nodes 5-10.

Essentially you have a massive windows cluster with pockets of availability groups defined throughout.


It's perfectly valid to have multiple AO groups, as long as each group conforms to the AlwaysOn constraints


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