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I was doing some tests with my two instance's of SQL Server 2008 R2 and 10 Mbps limited LAN. I setup synchronous database mirroring. Database log file is 25000 MB and 99% free before the test.

I started to move some records and rebuild every index in database, that took 2 hours and 7 minutes. For the last hour in that test the network utilization was 99% used, before that the usage was up and down. Immediately after test ended (2 hours and 7 minutes) the network utilization went to 0%.

After these actions database log file is 23% free which means that this test generated 19 GB of log records.

How can 19 GB of log records be transferred to mirror instance if my network has 10 Mbps? 10 Mbps has 1.20 MB/s which means it would take than 4 hours to transfer all that data?

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It depends on how you configured mirroring, synchronous or asynchronous (or something else, like log shipping, which isn't "mirroring", but some people lump it in anyway). –  Chris S Dec 10 '10 at 16:21
    
chris S, I'm using synchronous database mirroring. –  Geo Dec 11 '10 at 13:47
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How can 19 GB of log records be transferred to mirror instance if my network has 10 Mbps? 10 Mbps has 1.20 MB/s which means it would take than 4 hours to transfer all that data?

Sio the result of that is: 10mbit is not feasible.

Actually you forget compression. Log files are by no means space efficient.

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Yes I believe what you are looking for is what Tom states. Compress an SQL Log File (or Log File Backup if you like) into a Zip file and see how much space difference there is. SQL 2008 come a long way from where SQL 2000/2005 were in terms of data compression expressly for purposes like mirroring. In fact this is one of the features they tout as to why they are able to offer more robust site to site mirroring whereas in previous versions mirroring was generally only considered acceptable intrasite. –  Charles Dec 10 '10 at 17:36
    
Thanks TomTom, Charles, seems like this is an answer. Before sending data to mirror instance SQL compresses the content ... –  Geo Dec 11 '10 at 13:48
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