Alwayson on WSFC - is shared disk really not needed ?

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Alwayson on WSFC - is shared disk really not needed ?

szejiekoh

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August 22, 2016 at 6:26 am

#329662

Hi all,
I have read the stairways to alwayson series.
I have also understood alwayson does not need any shared storage resource.
But Alwayson sit on WSFC (assume it is a 2 node WSFC) - surely WSFC would need a shared disk (voting/witness) for maintaining quorum ?
So a shared disk is needed after all for maintaining quorum in the event of a 1 node failure (out of the 2 nodes available) to keep the cluster running isn't it ?
hence, shared disk is still a requirement isn't it ?
Am i getting it wrong ?
Regards,
Noob

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Gail Shaw SSC Guru Points: 1004504 More actions · Answer 1

Always On is a marketing term that encompases multiple features.

Always On Windows Failover Clustering required shared storage, just like clustered SQL instances always have.

Always On Availability Groups does not require shared storage, it's the sucessor to database mirroring.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 2

GilaMonster (8/22/2016)
Always On is a marketing term that encompases multiple features.
Always On Windows Failover Clustering required shared storage, just like clustered SQL instances always have.
Always On Availability Groups does not require shared storage, it's the sucessor to database mirroring.

Hi Gila,

Thanks for your reply.

But what I meant is "even though AlwaysOn Availability Group does not required share storage, but it requires/sits on WSFC" -> and a 2 Node WSFC require at least a shared disk for quorum right ?

-- i am not referring to Alwayson FCI, but just normal AlwaysOn with primary and standby replica sitting on each node in a 2 node WSFC - the WSFC require a share disk for quorum right ?

Regards,

Noob

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

Avbailability Groups do not require shared storage. Recommended quorum model is either node majority or node and file share depending how many nodes you have.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 4

GilaMonster (8/22/2016)
Avbailability Groups do not require shared storage. Recommended quorum model is either node majority or node and file share depending how many nodes you have.

Hi Gila,

Please let me know if i am wrong ->

i) AlwaysOn availability group must sit on WSFC cluster right ?

ii) and a 2 Node WSFC cluster require some sort of disk witness / fileshare for the quorum right ?

Regards,

Noob

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 5

Yes, it must be on a cluster.

As I said above, recommeded quorum model is either node majority or node and file share depending how many nodes you have (you need an odd number of voters). Node and disk majority or disk only are possible, but they're not the recommended configuration.

https://msdn.microsoft.com/en-us/library/hh270280.aspx

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 6

GilaMonster (8/22/2016)
Yes, it must be on a cluster.
As I said above, recommeded quorum model is either node majority or node and file share depending how many nodes you have (you need an odd number of voters). Node and disk majority or disk only are possible, but they're not the recommended configuration.
https://msdn.microsoft.com/en-us/library/hh270280.aspx

Hi Gila,

Thanks for your confirmation.

I wanted to sort this out because people are telling me that you can have a 2 node window cluster setup without any form of share disk at all. I am thinking how does the cluster achieve quorum then ?~

Can you shed some light on why is it not recommended to use a 2 node WSFC + shared disk witness ?

Regards,

Noob

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 7

szejiekoh (8/22/2016)
I wanted to sort this out because people are telling me that you can have a 2 node window cluster setup without any form of share disk at all.

Those people are correct. A SQL Server clustered instance requires shared disks (the DB files are stored on the shared disk), but Windows failover clustering, which is all that Availability Groups needs, doesn't.

Can you shed some light on why is it not recommended to use a 2 node WSFC + shared disk witness ?

Did you read the link I posted?

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Beatrix Kiddo SSC-Dedicated Points: 32407 More actions · Answer 8

Check out Perry Whittle's Stairway to AlwaysOn, especially this bit.

http://www.sqlservercentral.com/articles/cluster/107539/

Perry Whittle SSC Guru Points: 234024 More actions · Answer 9

szejiekoh (8/22/2016)
But Alwayson sit on WSFC (assume it is a 2 node WSFC) - surely WSFC would need a shared disk (voting/witness) for maintaining quorum ?

If your WSFC only has 2 nodes and they are in the same datacentre, then yes a disk witness would make sense and yes it would need to be shared storage presented to both nodes and added as a resource in the cluster.

szejiekoh (8/22/2016)
So a shared disk is needed after all for maintaining quorum in the event of a 1 node failure (out of the 2 nodes available) to keep the cluster running isn't it ?
hence, shared disk is still a requirement isn't it ?
Am i getting it wrong ?
Regards,
Noob

Quorum is the most complex part of the WSFC and the part that confuses people the most. Ideally your WSFC should contain an uneven number of nodes. In this situation the cluster would use the Majority Node Set quorum model, where each node has a vote in the cluster.

When you have an even number of nodes and the servers are same site then it is acceptable to use a shared disk, which requires shared storage.

If the servers are across datacentres you do not want to be replicating your quorum disk across sites so you would use a fileshare witness resource which would ideally sit on a separate site altogether.

Does this make sense?

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"Ya can't make an omelette without breaking just a few eggs" 😉

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 10

GilaMonster (8/22/2016)
szejiekoh (8/22/2016)
I wanted to sort this out because people are telling me that you can have a 2 node window cluster setup without any form of share disk at all.
Those people are correct. A SQL Server clustered instance requires shared disks (the DB files are stored on the shared disk), but Windows failover clustering, which is all that Availability Groups needs, doesn't.
Can you shed some light on why is it not recommended to use a 2 node WSFC + shared disk witness ?
Did you read the link I posted?

Hi Gila,

Thanks for your reply. I did read the link you posted but it didn't mentioned why a disk witness is not recommended.

Actually, what i am trying to clarify is that a 2 node WSFC will still need share disk (fileshare aside) for voting/quorum even though always on availability group sitting on top of it doesn't require any form of share storage -> am i wrong to say that ?

Regards,

Noob

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 11

Hi Perry,

Thanks for your explanation! We are all reading your stairways to alwaysOn ;)!

Base on your replies, can i said that

AlwaysOn Availbility doesn't need shared storage, but it needs to sits on WSFC

WSFC need a shared disk for its quorum if 1) it is having an even amount of nodes and 2) sit in the same DC/fileshare not an option.

Is my understanding correct ?

Regards,

Noob

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 12

szejiekoh (8/23/2016)
Actually, what i am trying to clarify is that a 2 node WSFC will still need share disk (fileshare aside) for voting/quorum even though always on availability group sitting on top of it doesn't require any form of share storage -> am i wrong to say that ?

It needs a third something for quorum. That something can be a file share or a disk witness. It does not have to be shared storage. A 2-node WSFC can work perfectly well with no shared storage at all, using a file share for the third voter.

It's starting to sound like you're pushing for someone to say you're right and the other person (who said that no shared storage is needed) is wrong.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

szejiekoh SSCarpal Tunnel Points: 4155 More actions · Answer 13

GilaMonster (8/23/2016)
szejiekoh (8/23/2016)
Actually, what i am trying to clarify is that a 2 node WSFC will still need share disk (fileshare aside) for voting/quorum even though always on availability group sitting on top of it doesn't require any form of share storage -> am i wrong to say that ?
It needs a third something for quorum. That something can be a file share or a disk witness. It does not have to be shared storage. A 2-node WSFC can work perfectly well with no shared storage at all, using a file share for the third voter.
It's starting to sound like you're pushing for someone to say you're right and the other person (who said that no shared storage is needed) is wrong.

Hi Gila, thanks for clarifying. Please do not get me wrong ;[, i just wanted to confirm that some sort of share resource is still required for AlwaysOn availability group (because it is residing on a 2 node WSFC - and the WSFC needs quorum)

I apologized if I have given you that impression.

Regards,

Noob