September 24, 2008 at 5:37 am
An architecture question, just looking for the broadstrokes really...
If I have an Asych mirror in SQL 2008, I read somewhere that in the event that I have to move to the mirror database, the client machine would require no reconfiguration.
Now I undertand this is possible in SQL 2005 with the SNAC? But is it now possible to achieve this with no SNAC? Simply using the existing DSN ODBC/OLEDB connection on the client machine. (This could help me in convincing a customer to upgrade to SQL 2008 from SQL 2000 for instance)
The only way i can currently achieve this is to recommend usiing 3rd party tools such as DoubleTake, where the server/instance name is available on a target server in the event of a source server problem.
I like the idea of mirroring but when a customer has many different ways of accessing his SQL Servers ie web servers and client machines in many disperate places where touching them is time consuming, it doesn't seem to fit the requirement.
Could you comment also include Sych with witness too 🙂
Any help appreciated....
Thanks in advance
November 1, 2008 at 10:23 am
IF you have clients with no SNAC, you might want to have them connect to an FQDN, something like sql.mydomain.com, with a short TTL. Then if you need to fail over, you can make the chance in your DNS server and get them to move to the new server. You can also have clients flush DNS to get them quicker.
Or you'd have to have each client change their ODBC/connection string to get to the new server. That's more complicated. You can change the IP of the new server to that of the old, but that gets more complicated, ARP tables, etc. can cause issues.
There are tricks you can play, and they're all tricks. The SNAC doesn't do anything magical. It has 2 entries and if one doesn't work, it tries the next one. You could do that if you have control of the app code. You can just retry on a second string if the first one is down. Be careful here because you don't want people connecting to both servers and updating data in wo places. Make sure one is always "recovering"
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