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Hyper-v disk controller

Posted on 2012-03-27
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Last Modified: 2012-03-27
I have a Windows 2008 server running Hyper-V
The Host server has SAS drives.
I have a virtual machine that is running without problems.
The Hard Drive controllers for this virtual machine on the Host server are setup as IDE (there are 2 of them, each with .vhd's)
Will I get better performance if I shut down the virtual and change these controllers to SCSI?
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Question by:ie0
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by:dlethe
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Yes, but "better" is relative.   If you aren't I/O bound then you won't see any difference.  (Don't expect anything major)
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by:Andrew Hancock (VMware vExpert / EE MVE)
Andrew Hancock (VMware vExpert / EE MVE) earned 250 total points
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SCSI may be better, BUT changing to SCSI now may cause your VM issues.
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by:ie0
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Han, is it not 'recommended' to change from IDE to SCSI if you are saying there may be VM issues?
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by:Andrew Hancock (VMware vExpert / EE MVE)
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Correct. If you change now, and restart the VM, you are likely to experience a BSOD.
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by:Cliff Galiher
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The performance between the SCSI virtual driver and the IDE virtual driver is negligable, as they have both been optimised to pass through regardless, and the performance will still be primarily dictated by your physical adapter.

Also notable, your system partition *cannot* be on a virtual disk attached to a virtual SCSI controller. It is not bootable.

-Cliff
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dlethe earned 250 total points
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Think of it this way.  You are redoing disk configuration, controllers, drivers, topology, enumeration, boot device, any cold-metal recovery software ...  If this was a non-virtualized system, do you have anything on the system that would care?   (P.S. Serial numbers of the disks would change and this could break some software that looks at the hardware for licensing.  Certainly MSFT uses disk type in their validation algorithm)

Personally, I wouldn't do this unless I had a lot of time and a few percentage points of I/O performance would be desirable, and I made a copy of the entire VM so I could go back if there is a problem.

Remember this answer and just make the next VM you create use SCSI emulation.
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