October 3, 2008 at 4:24 am
DNA (10/3/2008)
With mirroring the servers can be physically located near each other but they can also be at different sites. If they are at different sites this will protect against failure of the server and/or loss of disk at the primary site.
You can, but you have to watch the network load. I've seen a synchronous setup with servers in different physical locations (about 20 km apart) that did not work because the transaction load was more than the network link could handle.
It's better in 2008, since the log records are compressed before been sent.
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
October 3, 2008 at 4:53 am
There is a MS white paper called "MS WP DatabaseMirroring.doc"
It contains a nice overview of all sqlserver replication techniques and when to use them.
This is a "hear say" :the only technology that is not loosing connections at controlled failover time is the latests version of VMWare (which produces a memory footprint and moves that to the other node (equal hardware))
A problem with mirroring sql2005 is if the mirror connection has been broken and it needs to process the backlog.
It isn't easy to find out how much it still has to process, is it processing backlog, ....
Also keep in mind the witness should have its own power circuit, redundant network, (i.e. not used by the other partners) because if a partner fails, a quorum (=connection) has to be made between the witness and the remaining partner. If that is not possible, the database is not available
Also keep in mind not all vendor softwares support db mirroring (it needs the extra ";failover partner=..." in the connection string.
(e.g. MS SCCM)
Another usefull doc "SQL2005_DBM_Best_Pract_mirroring.doc"
I haven't got the urls right now, but I'll add them later on.
http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx
www.microsoft.com/technet/prodtechnol/sql/2005/technologies/dbm_best_pract.mspx
And off course the ever lasting BOL as great info !!
Johan
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October 3, 2008 at 7:21 am
Thanks for the information everyone. I've typically found Books Online to be good with academic knowledge but not very good on insight as to how or when to use the technology so that's why I came here.
The application is our own application using .Net and connecting with the SQL Native client provider, so if we have to modify our connection strings it wouldn't be too bad. (our connection strings are actually configurable since each client has it's own separate URL and separate databases)
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