Since moving to qemu 6.1.0 we've been seeing disk failures inside a qemu guest VM. This happened when using if=virtio on a host /dev/nbdX device. Binary searching on qemu commit history, I found these errors start on this commit:
Commit 18473467 file-posix: try BLKSECTGET on block devices too, do not round to power of 2 The above commit switched posix block device limits (including host /dev/nbdX devices) to query limits from /sys/dev/block/..., instead of using predefined limits. The scsi-generic driver was changed to use the queried limits, whereas the virtio-blk driver was only the queried max_iov, but still using the predefined max_transfer, which is unlimited in qemu. For NBD devices, max_iov is unlimited by the kernel nbd driver. As as consequence, the virtio-blk merged requests over the limit of our host /dev/nbdX device, which apparently caused the guest disk errors. The solution that worked for me was to change the virtio-blk driver to use the max_transfer limit queried from the posix host device (given by blk_get_max_hw_transfer). Or Ozeri (1): virtio-block: switch to blk_get_max_hw_transfer hw/block/virtio-blk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.25.1
