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How many mirrrored databases can I have on a server?
10 mirrored databases per server is the recommendation for a 32 bit computer WITH 4 processors or less. 64 bit computers have twice as many threads which means, in theory, that you can have twice as many mirrored databases. Also more processors = more threads = more mirrored databases.
|
|
32-bit |
64-bit | ||
| Number of CPUs |
Default # of Threads |
Mirrored Databases |
Default # of Threads |
Mirrored Databases |
| <= 4 processors |
256 |
10 |
512 |
20 |
| 8 processors |
288 |
11 |
576 |
22 |
| 16 processors |
352 |
13 |
704 |
27 |
| 32 processors |
480 |
18 |
960 |
37 |
Others are correct to point out that this is a recommendation, not a hard limit. What your server can actually handle depends on the architecture as well as the amount of other traffic being handled by the server.
Please note that this is merely an interpolation of the "official" recommendation originally recommended for database mirroring limits in SQL Server 2005 Books Online. This is not a statement of how many databases you should expect to be able to mirror on any given server. The actual number of databases you can mirror should be much higher than this and relies on many different factors.
For a more complete understanding of how to calculate the number of databases you can mirror on a given server, I recommend reading and investigating the information documented by the SQL Cat team: Mirroring a Large Number of Databases in a Single SQL Server Instance. As always, be sure to test your planned set up with a realistic workload.
Posted by Anonymous on 2 April 2009
Here are some notes on “SQL Server 2008 Database Mirroring” I took while attending an advanced class
Posted by Gé Brander on 12 June 2009
When you state 'processors' do you mean cores or processors? Do I need a 32 processor with quad cores ==> 128 cores or 8 processor with each 4 cores ==> 32 cores?
Posted by Robert Davis on 14 June 2009
I use the term "processors" to mean logical processors. It is the number of processors as SQL sees them. So if you have 8 quad core processors, then SQL sees 32 processors. If you have 32 quad core processors, then SQL sees 128 processors.
Posted by Gé; Brander on 15 June 2009
Ok, clear. Maybe adjust your post to Cores. It makes more sense to people. Then you make a clear distinction between processors and cores.
Posted by Robert Davis on 12 May 2010
Made some updates to the above post to clarify that the information presented is an interpolation of the official recommendation documented in SQL Server 2005 Books Online and not representative of a realistic expectation for mirroring limits of a server.
Posted by mark blakey on 1 October 2010
Do you think there is some advantage to enabling hyperthreading to maximise the number of databases that can be mirrored or is this just a false economy?