Server 2019 Hyper-V VHDX performance sucks for small files

blublub

Member
Dec 17, 2017
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Hello dear forum members

I just benched my virtual server and the VHDX which is meant for the file storage isn't performing very well.

The bare metal SSD RAID gets around 515MB/s for files sizes of 256kb and the VM only achieves 439MB/s - IOMeter 100% random read. The smaller the file sizes go the larger the difference gets - sadly I only have files smaller than 512kb.
The VHDX file is located on a dedicated array. I already have tested pass through mode to the VM and the IOBlanacer registry setting but performance stays the same.

Storage QoS is disabled in Hyper V. Both host and guest are Win server 2019 and the VM has plenty of resources.

Any ideas if I can improve that IO rates?
 

Deslok

Well-Known Member
Jul 15, 2015
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deslok.dyndns.org
what are the cluster sizes of the array's file system as well as the formated vhdx? is it a fixed size vhd or dynamically expanding?
 

blublub

Member
Dec 17, 2017
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what are the cluster sizes of the array's file system as well as the formated vhdx? is it a fixed size vhd or dynamically expanding?
Raid stripe size is 16kb for 9 ssds in a Raid 6. This stripe size was the fastest for my workload in the host. 32kb was similar but it declined at 64kb.
 

cesmith9999

Well-Known Member
Mar 26, 2013
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only a couple of settings for NTFS. the rest are system wide settings.

We were not using ReFS yet... so I do not have any optimizations for it.

Chris
 

blublub

Member
Dec 17, 2017
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only a couple of settings for NTFS. the rest are system wide settings.

We were not using ReFS yet... so I do not have any optimizations for it.

Chris
Ok.

I am starting to doubt ReFS. I have still seen quite some post with bad experience since 2018 which talked about colume corruption with disk being in "raw mode" and no means of repairing it - that would really suck.