Database Mirroring Limit

  • Comments posted to this topic are about the item Database Mirroring Limit

  • good timing steve, I was thinking about checking up on this very question this afternoon!

    the article says 32bit system so I presume 32 bit SQL on a 64bit OS would not have this limitation?

    IS there a limit with 64bit systems?

    looks like log shipping still has a role to play! 🙂


  • I heard early on that 50 databases was a limit, but I've not seen anyone running that far. I did see this blog ( where they mention a 64 bit OS flaking around 100 databases due to thread issues.

    5 threads per mirror seems like a lot. You can alter the worker threads, so that might help.

    Even with mirroring, I think you want to have log shipping for the delay. That can come in handy.

  • That is a good question George and one I cannot answer yet. I have not tested running 32bit SQL with database mirroring on a 64bit machine. Though the 10 database limit is only a suggested limit as I have a 32bit SQL Server on 32bit Windows mirroring close to 30 databases without issue.

    Now the databases are extrememly small and there isn't alot of traffic flowing in and out of them but you can successfully mirror more than the MS recommended 10.

  • thats good to know steve. I am sure I have seen threads on this site where people have said they are mirroring quiete high numbers of databases. I don't believe they stated whether they were 32 or 64 bit though.

    Perhaps people who are mirroring who come across this thread could post their experiences?


  • We mirror our customer's hosted databases in high performance mode. About 140 databases, from one server to a twin located on the same network switch. The purpose is simply to provide a very warm backup in case of hardware failure - much cheaper than clustering, and everything is redundant - not just the front end of the machine. The limitation is simply the number of worker threads on the mirrored machine. 5 workers per DB on the mirror, 2 workers per DB on the primary. On a 4 proc 64 bit machine the default number of worker threads is 512. We upped it to 1000 and have observed no problems at all. The mirror has very low CPU usage, the network traffic is minimal.

    Student of SQL and Golf, Master of Neither

  • Thx Bob for the insight.

    Jason...AKA CirqueDeSQLeil
    I have given a name to my pain...MCM SQL Server, MVP
    Posting Performance Based Questions - Gail Shaw[/url]
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