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Windows software mirroring - way to speed up rebuild

Posted on 2010-04-04
Medium Priority
Last Modified: 2013-11-14
I have a Windows 2008 server with two drives that are software mirrored.  After a recent power outage the drives were out of synch when the server came back up on power restore and automatically they started to resynch.  The drives are large and the synching is taking a long time and the system is slowed down as a result.  Is there any parameter that can be configured to speed up the resynching?  Please note that I understand that a hardware RAID would do this kind of thing faster but at this point I do not need suggestions which would involve that as a solution. I am looking only for any suggestions that would speed up software mirroring.
Question by:lineonecorp
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Accepted Solution

David earned 600 total points
ID: 29736205
Shut down every app that you can that would generate I/O.  Application software, logging, system services, every I/O that the windows machine performs during normal operations compete with rebuilding.

But in grand scheme of things, the biggest delays are courtesy of the type of disks you buy.  It is not unusual for a consumer class HDD to take up to 30 seconds to remap a failed sector.  Enterprise disks can be 10X faster.

Also hardware RAID will not necessarily do things faster.  If you have a hardware RAID controller with battery backed up write cache, then the firmware will certainly take advantage of it.   If, however, you think the benefit will come from extra CPU power, then you would be mistaken.  A modern CPU can easily do 6TB/sec which is the upper limit of the bus of RAID5 calculations and still have CPU power to do other things.


Assisted Solution

sukamto earned 600 total points
ID: 29739203
normally power failure wont break / fail windows software mirror. Is the hdd got hardware issue?
LVL 47

Expert Comment

ID: 29741932
Agreed, power failures will rarely break a mirror, but they will certainly generate, ECC errors, unrecoverable read errors, inconsistencies, stale drive shutdowns.  It is quite common that some clusters of "bad" blocks will show up.  If the rebuild process appears to halt for a few seconds to a minute, you hit one of them.  Unless both disks have problems reading the same physical block number, then nothing you can do on the windows side.  The recovery is a function of the drive hardware specs, not windows

Author Comment

ID: 29768719
The mirrored drives were 1 TB and the system restarted just before people got to work so the re-synching had already started and it was slowing people down but after a few hours  it seemed to go faster and it was less noticeable. If I would have had a chance I would have started the server without mirroring and then done it after hours.

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