Just a hunch, can you edit the VM disk and switch the disk's Async IO mode toWould anyone have any idea where should i look ?
threads(for cache = write back/through) or
native(for cache = off, none or direct sync), respectively.
We're currently looking into a potential regression with the new 5.13 Kernel and io_uring and (mainly, but potentially not limited too) VirtIO Block or SATA as bus controller, interestingly we can mainly reproduce such symptoms with using Windows, but it could be just easier to trigger that way or really a different issue. Anyhow, that's why it'd be interesting to see if switching Async Mode would help you.
Possibly also worth a try, but potentially not as straight forward as async mode switch: use SCSI for the disk bus (detach disk and re-attach by edit with SCSI). The dev name in the VM will change from /dev/vdX to /dev/sdX though.