[Qemu-devel] question about block size and virtual disks

[Chris Friesen]

Hi,

Suppose the host has a physical disk that only supports 4KB access, with no 512B 
fallback.

If we boot a guest with "cache=none", does the guest need to be able to handle 
disks with 4KB blocks or is qemu able to handle guests trying to access the disk 
with 512B granularity?

Also, does the 4KB block size get "passed-through" to the guest somehow so that 
the guest knows it needs to use 4KB blocks, or does that need to be explicitly 
specified via virtio-blk-pci.logical_block_size and/or 
virtio-blk-pci.physical_block_size parameters?  (Assuming I'm using virtio-blk-pci.)

Thanks,
Chris