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We are currently hosting a SaaS website on two Windows 2008 R2 / SQL Server 2008 R2 Servers. Would upgrading to SQL Server 2012 / Always On give us any advantages with respects to high availability?

Note that while we are looking for high availability, high performance is not really an issue for us at the moment, so being able to run read-only queries on backup database servers is not really important.

  • It looks as though as far as high availability goes, it's no better than a fully redundant clustered system. So if you have a good clustered system, then stick with it. However, I'm not really 100% sure about that, as my research is a bit thin (we won't be upgrading because the new licensing, combined with vmware's licensing change last year, left us with little budget for software upgrades) – Mark Henderson Feb 1 '12 at 19:31
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Readable Secondaries: you can query the 'mirror'. See AlwaysOn: High-Availability and reads Scale-Out.

  • This might be an advantage for those who need high performance but, as already noted, this is relevant for us since our database server is idling anyway. – Adrian Grigore Feb 2 '12 at 12:34
  • Secondary Backups then perhaps – Remus Rusanu Feb 3 '12 at 4:24
  • it is an advantage, but only if you have more than two nodes, which would not be the case for us. – Adrian Grigore Feb 4 '12 at 7:59
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My understanding is that AlwaysOn is a shared nothing configuration. Brent Ozar kinds confirms this and extends it by saying that it doesn't require the same hardware.

Here's his writeup (from a few years ago, actually).

http://www.brentozar.com/archive/2010/11/sql-server-denali-database-mirroring-rocks/

Here's the BOL for AlwaysOn

http://msdn.microsoft.com/en-us/library/ff877884%28v=SQL.110%29.aspx

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    But Mirroring with SQL Server 2008 R2 works just as well on different hardware. One of our servers runs on an Intel CPU, whereas the backup is using an AMD CPU. – Adrian Grigore Feb 2 '12 at 12:36
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I think there's a big advantage for people who target the database mirror - maybe not applicable in your scenario, since you're just connecting internally, but worth noting. When the cluster manager controls access, you have a single IP and DNS name that always points to your primary node, whichever node that is. To take advantage of mirroring, your client has to be mirror-aware (like the SQL Native Client is, but the OLDDB SQL client is not). With AlwaysOn, you can use any client or connection method you want and it will fail over to the active node as needed - you don't get the advanced features like readable secondaries without the native client, but at least it's something.

In your case, though, I'd agree that it doesn't provide anything particularly compelling.

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