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What is the AlwaysOn equivalent of Database Mirroring's Witness
I've got some experience in setting up new synchronous Database Mirroring environments, and have done some awful, awful things in the past to get an asynchronous reporting database replica, while within the budgetary constraints for Standard edition. But I'm now part of a new project which has both HA and TDE as requirements, so we have the budget for Enterprise. This gives me an opportunity to look at AlwaysOn. While trying to get my head around the varying differences, what I can't seem to find is the equivalent of the Witness. Our existing Mirroring endeavours have always used Express to provide the Witness (for cost savings) but, as I understand it, only Enterprise can take part in AlwaysOn. I can't see how anyone could expect me to have run an extra Enterprise node just to provide quorum so, given a provisional setup of: * 2 x synchronous, auto-failover OLTP nodes * 2 x asynchronous, read-only reporting nodes * 1 x quorum-providing something ...what is 'something'?
Since Availabilty Groups are based Windows Failover clustering you have the choice of a disk or fileshare quorum. The choice depends on a couple of factors: 1. Are your servers in one datacenter or geo placed? 2. Number of datacenters? 3. Physical or Vmware? Chosing the Quorum is complex and I read somewhere that Allen Hirt (HA guru) dedicated over 100 pages in his new book on the topic. And since you are asking a basic question about this I guess you should really (really) read up on AAG's. It is a complex topic with a lot of gotchas. Links: [AAG Video of Real Life Lessons Learned - Brent Ozar][1] [Brents AAG articles repository][2] <- Check out the setup checklist for AAG, it is really good and will help you out a lot! [Allen Hirt's FAQ on the topic][3] [1]:
http://www.brentozar.com/archive/2013/07/alwayson-availability-groups-real-life-lessons-learned-video/ [2]:
http://www.brentozar.com/sql/sql-server-alwayson-availability-groups/ [3]:
http://sqlha.com/2012/04/13/allans-alwayson-availability-groups-faq/
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