What is "kvm: Desc next is 3" indicative of?

[Gektor]

There is no choice for me to compare performance, in my case VirtIO SCSI is absolutely unstable.

 

[davemcl]

When you switched the disks from Virtio SCSI to VirtIO Block and changed the SCSI Controller did you need to re-initialize the disks in Windows guest (assign the drive letters again) or did Windows figure it out on its own?

@Max2048
When I did this on a test VM the C: drive was fine, the D: drive required initialisation.