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Hyper-V 2012 R2 and Storage QOS

Posted on 2014-01-06
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Last Modified: 2014-11-12
Hello ,


Im testing the Storage QOS feature of Hyper-V 2012 R2 .

As we know a simple SAS disk has about 120-150 IOPS max.

So i have a Virtual Machine and i have limit it to 150 iops.

The results i take are far worst from a physical disk with the same IOPS. Copies are veeeery slow and also if i try to copy something and in the same time try to open lets say control panel everything becomes unresponsive until the copy finishes. If i remove the qos everything works great.

Is this standard behavior ?

Thanks
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Question by:Anestis Psomas
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LVL 119
ID: 39761446
I would not expect to see the IOPS in a virtual machine to equal the maximum number of IOPS for a single physical disk, because the I/O is virtualised inside the VM.

e.g. the virtual disk (vhd) is created on the pyhsical disk, and you are testing inside the VHD.

So I would not consider this to be strange but completey normal.
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Author Comment

by:Anestis Psomas
ID: 39761483
Hello ,

Maybe you are right in case i have my VM stored inside a single physical Disk .

In my case i have a Fibre SAN with multiple disks and a lot of IOPS .

Also if we do not expect to see the IOPS of a physical disk then what do we expect? The term IO  is the same in physical and virtual disks.

Thanks for your help .
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LVL 119

Accepted Solution

by:
Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 39761567
Physical I/O and Virtual I/O is less.

Also the VM which is under a hypervisor will also perform worse, than if the server was physical.

What you can expect, is that it will be less, and not equal to physical I/O performance.

If you want physical I/O performance, present the disks via RAW Mapped LUN.
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Author Comment

by:Anestis Psomas
ID: 39761592
So if i want to emulate the iops of a physical SAS disk how much iops i must give to a VM ?


Thanks
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LVL 119
ID: 39761604
if you have a single physical SAS disks, e.g. 100 IOPS (after calculating), you would need to give the VM, 100 IOPS.

But this may require you to, use RAID and JBOD techniques to increase the datastore IOPS.
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Author Comment

by:Anestis Psomas
ID: 39761749
The storage i use for my tests of qos is a 3PAR Storeserv . I have present cluster volumes to my cluster from this storage. This is a fibre channel storage and it can give me maximum 16000 IOPS .

Thanks
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LVL 119
ID: 39761761
So that should be plenty for your VM.
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Author Comment

by:Anestis Psomas
ID: 39761810
Hello ,

of Course its plenty but this is not the point of the conversation .

 As i write earlier the question is why the 150 iops limit i put into the VM doesn't have the same behavior with 150 iops on a physical disk as the IOPS as a metric is identical in both Virtual Hard Disk and Physical Disk.
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LVL 119
ID: 39761818
Okay, I think I undersatand you have limited a VM to 150 IOPS

How is the copy being performed across the network?

or local file copy?
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Author Comment

by:Anestis Psomas
ID: 39761827
It is a local file copy .
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