On Tue, Apr 05, 2016 at 02:31:53PM +0200, Laszlo Ersek wrote:
On 04/05/16 06:25, James Shimer wrote:
I've been doing some testing if KVM with 4K physical sector virtio disks and they work with KVM as a none boot disk. We'd like to be able to boot a 4k physical sector disk in KVM, is there 4K support in any seabios newer/upcoming releases, or is there a way to configure for 4k sectors?
reference from master src/hw/virtio-blk.c lin 142
if (vdrive->drive.blksize != DISK_SECTOR_SIZE) { dprintf(1, "virtio-blk %pP block size %d is unsupported\n", pci, vdrive->drive.blksize); goto fail; }This code dates back to 4030db0d2c5a7.
I'm not an expert, but I think BIOS interfaces don't support a sector size different from 512 B. It seems that a drive with 4096 B physical sectors should enable (the emulation of) a 512 B logical sector size, so that it can work with code that assumes an 512 B sector size.
The EDD standard ( https://en.wikipedia.org/wiki/Enhanced_Disk_Drive ) allows for 4K blocks. However, the older BIOS interface (eg, int 1301) only support 512 byte sectors. This means that the BIOS would need to emulate 512 byte reads should one of the older interfaces be called on one of these drives. This isn't difficult as SeaBIOS already does this for cdroms.
I guess for a virtio-blk disk, that means:
-device virtio-blk-pci,physical_block_size=4096,logical_block_size=512
In practice, almost all real drives seem to do the above. So, adding support for drives that don't has not previously been a priority.
-Kevin