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I've just installed my new M4 256GB on a Windows Server 2008 R2 Hyper-V server.

On the host system using Crystal Disk Mark I've got 212 Mb/s as 4k QD32 write performance, but when I create a VHD disk on the SSD and test using the same configuration on a guest Windows Server 2008 R2, I get 7 Mb/s, i.e. about 30 times slower.

Any hint?

Of course Fixed size vhd

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Fixed or Dynamic VHD? If you want performance you'll have to pass the disk through to the VM; there will always be a performance hit with VHD files. – Chris S Jul 5 '12 at 12:37
Yes and no - seriously, 7Mb/s is stoo low, even with dynamic VHD. I get 10 times that with NO ssd on a 8 Velociraptor array. 7 is simply too slow. – TomTom Jul 5 '12 at 14:12
Mb or MB? There's a big difference. – MDMarra Jul 5 '12 at 15:32
@MDMarra: in this instance the difference between 7Mb and 7MB is academic, both are preposterously slow. – ThatGraemeGuy Jul 5 '12 at 15:39
@GraemeDonaldson Agreed, but too many people use Mb when they mean MB. We're supposed to be professionals here, I don't think it's too much to ask that the OP uses the correct units :) – MDMarra Jul 5 '12 at 16:38

I'm currently experiencing very slow disk I/O and massive disk queues of 100+ on a guest whilst the host performance is fine. I'm not running SSDs but also Server 2008 R2 with fixed VHDs.

Not sure if this applies to you or not, but I'm investigating it as an option:

This slideshare article also mentions offsetting your partition. I'm not sure if this is required for Server 2008 and above though.

The article links to these pages for more info:

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The partition offset isn't an issue unless he created the partitions outside Windows 2008+ or the Windows Installer for 2008+. It automatically aligns partitions on 1MB boundaries. – Chris S Jul 5 '12 at 15:31

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