Im running a Linux (PopOS) VM on my Unraid server and have noticed a large performance difference between shares and vdisks.

 

The vdisk is passed to the VM as follows:

<disk type='file' device='disk'>
  <driver name='qemu' type='raw' cache='writeback'/>
  <source file='<path_to_the_vdisk>' index='2'/>
  <backingStore/>
  <target dev='hdc' bus='virtio'/>
  <boot order='1'/>
  <alias name='virtio-disk2'/>
  <address type='pci' domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
</disk>

Note: The vdisk is stored on the array (not the cache drive)

 

Shares are passed to the VM as follows:

<filesystem type='mount' accessmode='passthrough'>
  <source dir='<path_to_the_share>'/>
  <target dir='<share_name>'/>
  <alias name='<share_alias>'/>
  <address type='pci' domain='0x0000' bus='0x05' slot='0x00' function='0x0'/>
</filesystem>

And then mounted with fstab like:

<share_name> <path_inside_vm> 9p trans=virtio,version=9p2000.L,_netdev,rw 0 0

Note: The share has caching set to "Yes".

 

Drive info:

Array: 2x Samsung 870 EVO 4TB (one for parity)

Array file system: xfs

Cache: Samsung 970 EvO Plus 1TB

Cache file system: btrfs

 

I tested the read and write speeds by copying a large file. Here are my results.

share -> share: 27 MB/s

vdisk -> vdisk: 600 MB/s

share -> vdisk: 56 MB/s

vdisk -> share: 48 MB/s

 

Why is the share performance so much worse than the vdisk performance? Do you have any suggestions on how to get better share performance?

 

 

Did you find anything out? My performance is terrible. I get about 12mb/s trough the share which has normally about 150mb/s. Whats wrong here?