May 14, 2013 at 6:47 am
Is it possible to setup DB mirroring between SQL 2005 as primary and SQL 2008 R2 as Mirror.
May 14, 2013 at 7:30 am
Yes, but it's an exceedingly bad idea and it's only supported as part of a rolling upgrade process.
The mirroring will work, however if that ever fails over then the new principal is 2008 R2 and the mirroring will go suspended and you won't be able to resume without upgrading the 2005 server.
Essentially it's a failover implementation that you can never ever fail over, kinda pointless.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
May 14, 2013 at 7:49 am
I have never tried that but first prerequisite for that as per MS :-
"For a mirroring session to be established, the partners and the witness, if any, must be running on the same version of SQL Server."
http://msdn.microsoft.com/en-us/library/ms366349.aspx#Prerequisites
May 14, 2013 at 8:26 am
It is possible to have the mirror a higher version, but as I said it's a stupid thing to do and iirc it takes extra work to even set up that way, you can't use the GUI to set it up.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
May 14, 2013 at 10:18 am
GilaMonster (5/14/2013)
It is possible to have the mirror a higher version, but as I said it's a stupid thing to do and iirc it takes extra work to even set up that way, you can't use the GUI to set it up.
The only practical use I can see is to setup a database for upgrade prior to actually implementing the upgrade; saves a bit of time in your maintenance window for the upgrade by not having to perform a full restore?
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May 14, 2013 at 2:24 pm
About the only use is as part of a rolling upgrade, so install a second SQL instance (same version), configure mirroring, make sure everything works and the app redirects properly, upgrade the mirror (now running higher version mirror than principal), fail the mirroring over, upgrade the principal, fail the mirroring back (or, if you're migrating hardware as well, leave the 'mirror' as the new principal).
Version upgrade with minimal downtime (one or two failovers).
In a rolling upgrade though you wouldn't install the mirroring with mismatched versions, it would just be that way for a brief time during the upgrade.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
May 14, 2013 at 8:31 pm
GilaMonster (5/14/2013)
It is possible to have the mirror a higher version, but as I said it's a stupid thing to do and iirc it takes extra work to even set up that way, you can't use the GUI to set it up.
Gail,
I don't think it's so stupid, I think it depends.
I "migrated" a huge, very big database, from SQL 2005 to SQL 2008 using mirroring. It took just few seconds of downtime, literally speaking and was just changing the code. It went very well.
Backup and restore was not an option to me, too much downtime.
Of course, I knew going back was not an option, but that was actually part of the initial plan.
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