Maximum Number of Mirrored Databases Decreases as Number of Available Cores Increases?

Question

Hi,
I wonder if you can help me. We're planning a large in-house mirroring deployment and are concerned we may (at some point) run into the limits described in the following KB article:
http://support.microsoft.com/kb/2001270/en-gb.
Based on the formulas contained within the above article, I knocked up a quick spreadsheet to see how increasing the number of cores might allow us to increase the number of mirrored databases. However, to my surprise, my calculations imply that as you increase
the number of cores, the number of databases you can potentially mirror decreases?
No. of Logical Cores
Max Worker Threads
Threads Required per Mirrored Database
Max. No. of Databases that can be Mirrored
4
512
3
170.6666667
8
576
4
144
12
640
5
128
16
704
6
117.3333333
20
768
7
109.7142857
24
832
8
104
28
896
9
99.55555556
32
960
10
96
64
1472
18
81.77777778
Am I missing something here? Have a miscalculated somewhere? This seems counterintuitive.
Regards
Andy

Answer 1

Hi  rushandy,
As the KB post, we need to calculate the max worker threads, which is default no. of worker thread SQL Server will spawn. about database mirroring requirements for worker threads, we need to calculate the number of threads required per mirrored database.
At end,
maximum number of databases that can be mirrored = the max worker threads/ the number of threads required per mirrored database.
As your post, for 64 bit architectures, if the number of logical CPU cores is 16 on the mirror server, after calculating , maximum number of databases that can be mirrored is 117. However, in actual scenario, the mirroring databases is less than 117, or
else, it will cause some errors, such as error 17884 and so on.
Usually, not all worker threads would be available to perform mirroring activities as some threads are assigned to core database activity on the server. For more information, see：http://sqlknowledgeshare.blogspot.com/2012/02/do-you-know-maximum-number-of-databases.html
Regards,
Sofiya Li
Sofiya Li
TechNet Community Support