VM Share performance

[MichaelBernasconi]

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?

 

 

[unifiedmamba]

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?