VM disk performance during host copy

[jbartlett]

I have a Win8 VM running on my cache drive. When I'm copying large files to the cache share, the VM performance bottoms out and Task Manager shows the drive activity lit up to 100%.

 

Is it possible to allow the unraid disk driver to play nice with VM disk access?

[jonp]

Ssd or hdd based cache drive?

[jbartlett]

HDD. The copy was happening on the system itself, via mc.

 

I was getting around 150mb/sec transfer and the VM was absolute shit as far as performance goes. Copying a file at 75mb/sec had a lot more grace.

 

I do understand that writing to a HDD does affect other processes also read/writing. Just wondering if there was a "nice" option or priority for drive I/O like there is for multi-threading applications.

 

HD Tune was reporting less than 2mb/sec transfer rate when the copy was 129mb/sec

[BRiT]

Have you tried launching mc via nice or tried renicing the existing running process of mc?

[jbartlett]

Have you tried launching mc via nice or tried renicing the existing running process of mc?

 

The thought never occurred to me. I shall try!

[jonp]

Right now, we do not have any prioritization for VMs over other IO operations to a disk.  With SSDs in the cache, there is probably enough IO that it won't matter, but with an HDD, I can see how this would cause pretty abysmal performance.  Definitely something for the roadmap to improve how we handle that and there are definitely ways to do this.

 

Short term, BRiT's recommendation Should Work just fine, but I haven't tested it yet.  Another way would be to use a non-array device for your VM.