David,

How do your drivers handle a virtio-based CD-ROM?

qemu by default uses IDE, or can be configured to use SATA CD-ROM devices, however, OpenBSD's vmd(8) strictly uses a virtio-based CD-ROM.

I don't know how the interactions end up differing between hard drive and CD-ROM access in that case, but its something to look at if you weren't aware of it.

From OpenBSD 6.9 booted using vmd(8) on OpenBSD 7.0.

OpenBSD 6.9 (GENERIC) #464: Mon Apr 19 10:28:56 MDT 2021
...
virtio3 at pci0 dev 4 function 0 "Qumranet Virtio SCSI" rev 0x00
vioscsi0 at virtio3: qsize 128
scsibus2 at vioscsi0: 1 targets
cd0 at scsibus2 targ 0 lun 0: <OpenBSD, VMM CD-ROM, 001> removable
virtio3: irq 7