<filesystem type='mount' accessmode='passthrough'>
<source dir='/mnt/user/Recordings'/>
<target dir='recordings'/>
<address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
</filesystem>
recordings /mnt/recordings 9p trans=virtio,version=9p2000.L,nobootwait,rw,_netdev 0 0
1. Array disk
2. HDD
3. /mnt/user
4. SSD /mnt/cache (Qcow2 and Raw tested)
5. NA
6. BTRFS (Not sure if you mean the cache disk or the file system inside the VM. Ext4 filesystem inside VM)
7. Rsync
8. 75MB/s
Updated some info as it seems you changed the questions in the first post.