AlwaysOn Availability groups

September 1, 2012

I’ve setup a few SQL Server Mirroring and Log shipping solutions and have been keen to find out  what the ‘AlwaysOn’ availability groups was all about in SQL Server 2012.

It’s the successor to database mirroring.

I’ve always thought database mirroring was pretty cool and a step up from log shipping, it had its draw backs yes, but overall I’ve been pretty impressed by the whole thing. Turns out, it’s a bit like the short lived mini-disks players, short lived. Poor thing. It was introduced as recently as SQL server 2005 SP1 and now soon to be discarded and superseded by AlwaysOn Availability groups.

Log shipping on the other hand has survived. Ye ‘ol faithful!

Database mirroring is still available in SQL Server 2012, but it’s marked as a Deprecated Feature.

The below is a really high level quick overview of the new feature in the high availability stack in SQL Server 2012.

  • Multi database failover
  • Able to read the inactive node
  • Able to take backups on inactive nodes
  • Multiple nodes (1 x primary and up to 4x secondary/replicas)
  • It uses t-logs with compression
  • Based on Windows Server Failover cluster (but you don’t need any shared disks)
  • SQL Server nodes use local storage
  • There is no witness server, uses the WSFC quorum
  • Always ON must be on same domain

SQL Server 2012 AlwaysOn High Availability


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