October 29, 2009 at 10:34 am
We have database mirroring running in asynch mode over a WAN from London -> Paris. The speed, which I have tested by simple copying a large file and timing it, is about 7Mb/sec. I have tested the filecopy seperately to both the data and log file drives.
Unfortunately, the max restore rate we get is 3Mb/sec. This causes a massive backlog of up to 80Gb if unsent log which can take up to 10 hours to restore over to the mirror.
Are there any tweaks to improve the restore rate? IO is not the issue and we can't upgrade to SQL2008 just yet to take advantage of the compression.
cheers
thanks
SQL_EXPAT
October 29, 2009 at 11:01 am
I'm not aware of any way to get around this based on your circumstances. Did you check the wait stats / perfmon to identify the limiting factor? Assuming that nothing else is taking your bandwidth, it has to be something on the mirror server/database - you don't have snapshots against the mirror do you?
October 29, 2009 at 12:03 pm
No, the DR server is totally passive and we dont run any database or disk snapshots.
Murphys Law now that I want to pull some wait stats the server is 100% in synch. Once it lags again I'll pull some wait stats. Thanks for the tip - that may help me identify to cause.
thanks
SQL_EXPAT
October 29, 2009 at 1:51 pm
I bet it would go very much faster the other way around :w00t: :hehe:
Did you check these Database Mirroring Best Practices and Performance Considerations ? http://technet.microsoft.com/en-us/library/cc917681.aspx
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October 30, 2009 at 4:23 am
Ok, so at them moment I have an unsent log of 4090945 KB and current restore rate of 2574 KB/sec which gives me an estimated 25 minute lag.
Wait stats on Mirror show 84% of the waits on waittype DBMIRRORING_CMD:
From BOL:
"Occurs when a task is waiting for log records to be flushed to disk. This wait state is expected to be held for long periods of time."
I dont think this can be optmised any further....
thanks
SQL_EXPAT
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