IOPS capped on a VM within Hyper-V

Question

quick question ... we get 100,000 IOPS once we used SQLIO against a VHDX file . ( let's say disk2.vhdx) 
from inside a VM , we mount the same disk as a secondary disk and run SQLIO against it ; we get about 30,000 IOPS. 
There is no QoS for storage defined yet .. 
Is there any other limit ? we increased VM memory to 64 GB , processor to 8 and never went above 30,000 

Answer 1

Hi,
The Hyper-V storage stack also uses unbufferred writes to make sure that the writes from the guest bypass the underlying host filesystem stack. When you use the SQLIO you
should create a file as big as possible, so that you can exercise the entire disk. For hard disks, creating a small file causes the head movement to be restricted to a portion of the disk. Unless you’re willing to use only a fraction of the hard disk capacity,
these numbers show unrealistically high random IO performance.
The related information:
SQLIO, PowerShell and storage performance: measuring IOPs, throughput and latency for both local disks and SMB file shares
http://blogs.technet.com/b/josebda/archive/2013/03/25/sqlio-powershell-and-storage-performance-measuring-iops-throughput-and-latency-for-both-local-disks-and-smb-file-shares.aspx
The related KB:
Hyper-V storage: Caching layers and implications for data consistency
http://support.microsoft.com/kb/2801713
Hope this helps.
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