I noticed I was getting poor SSD (Crucial MX300) write performance (about 100 MB/s or less) in my Windows 10 VM. The SSD was mounted using Unassigned Devices. I noticed Windows referred to the VirtIO drive as a SCSI device. So I tried changing "Primary vDisk Bus" to SATA to see if it would help.   That didn't help, and it ended up causing other issues including stuttering/cracking audio.  The MSI fix doesn't seem to work.  Switching back to VirtIO doesn't allow Windows to boot.

 

What performance should I expect from my SSD?  Was my problem a VirtIO configuration issue?

 

EDIT.

Will try a fresh install and passing though the SSD.

 

Edited November 9, 20196 yr by Marc_G2

A problem with the default vdisk method is that the vdisk itself cannot be trimmed which means that performance will gradually suffer.  Try this:

 

https://forums.unraid.net/topic/51703-vm-faq/#comment-557606

 

I will give this a try before trying to pass though the SSD.  Although I was only using 50/500 GB I had available.

Well I managed to get VM booting with VirtIO again.  I needed to initialize my newly created disk in Windows Disk Management prior to switching the primary disk to use VirtIO.

 

A quick file copy test shows sustained writes are still less than 100 MB/s.   For some reason, Windows won't let me defragment the SSD.  It says "Optimization not available" on its status.  I'm pretty sure the XML is correct:

 

<disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback' discard='unmap'/>
      <source file='/mnt/disks/Crucial_CT525MX300SSD1_163213963944/Windows 10/vdisk1.img'/>
      <backingStore/>
      <target dev='hdc' bus='virtio'/>
      <boot order='1'/>
      <alias name='virtio-disk2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>

 

Edited November 9, 20196 yr by Marc_G2

Did you follow the directions in the link?  Does it show in Defrag as a Thin Provisioned Drive?

I believe the config is correct (see above).  The media type says it's a "Solid state drive" and doesn't say it's a thin provisioned drive.   So I'm not sure where I went wrong.

I created a new VM while passing though the SSD.  Sustained write speed is now 200+ MB/s.  Definitely better, but still not close to bare metal.  Crystal diskmark gave bad results due to caching.  For perspective, this is what Space Invader One got for a Vdisk.  He had similarly bad sequential write speeds.

 

https://youtu.be/QaB9HhpbDAI?t=15m44s

 

Should I still configure the disk to as a "thin provisioned drive"?