Lync 2013: Single Witness server for Multiple SQL pair
There are many great blogs available on all the Gotcha’s with Lync 2013 mirroring with witness. But what I encountered with it was not available in either one of them. So I decided to share my experience as well as workaround I used to fix it.
Can we use Single witness server for multiple pair of SQL server? Well as per TechNet Yes.
Here is what TechNet says: http://technet.microsoft.com/en-us/library/jj205248.aspx
If you use a witness, you can use a single witness for multiple pairs of Back End Servers. There is no strict 1:1 correspondence between witnesses and pairs of Back End Servers. Deployments that use a single witness for multiple pairs of Back End Servers are not quite as resilient as topologies with a separate witness for each Back End Server pair.
Above statement is very clear that we can use single witness for multiple pair of SQL servers. But it does not talk about if that is true in multiple central site environment.
There is one more public blog which I found is very interesting and it says following statement which is correct but I have a question on that.
1.) TechNet states you can use a single Witness for all your pools. This is correct, but if you have multiple central sites then Witness needs to be defined in each “Shared Components” under each central site or it will not show up as an option.
But my concern is will it allow you to add the same witness server as a shared component?
I tested it in my lab environment and the answer is no it does not allow.
Here is my environment
Enterprise pool: 3 FE server
Backend: SQL 1 and SQL2
Witness server: Witness1
I have mirroring Setup in SITE1 and Automatic failover works Great!
Enterprise Pool: 3 FE servers
SQL 3 and SQL4
Witness Server: (Decided to use the same witness server which is being used in SITE1)
Tried to Setup Mirroring with Witness
When I tried to setup mirroring in SITE2 as SQL3 Primary and SQL4 mirror with Witness1 as witness server (which is already being used for SQL1 and SQL2 in Site1), Topology builder will not allow me to add it under shared component. It gives following error.
“FQDN Already in use in Topology”
So, we need separate witness server for each Central site.
I didn’t had another server to use as witness for SITE2 so I created a CNAME entry for Existing witness (Witness1) and I was able to use that CNAME entry as witness server in SITE2. Mirroring with witness is setup fine and works great! J
Exchange and Lync Architect