Am Donnerstag 04 März 2010 14:20:17 schrieb Christoph Hellwig: > > Add a logical block size attribute as various guest side tools only > increase the filesystem sector size based on it, not the advisory > physical block size. > > For scsi we already have support for a different logical block size > in place for CDROMs that we can built upon. Only my recent block > device characteristics VPD page needs some fixups. Note that we > leave the logial block size for CDROMs hardcoded as the 2k value > is expected for it in general. > > For virtio-blk we already have a feature flag claiming to support > a variable logical block size that was added for the s390 kuli > hypervisor. Interestingly it does not actually change the units > in which the protocol works, which is still fixed at 512 bytes, > but only communicates a different minimum I/O granularity. So > all we need to do in virtio is to add a trap for unaligned I/O > and round down the device size to the next multiple of the logical > block size. > > IDE does not support any other logical block size than 512 bytes.
We did that because we wanted to use DASD devices, which have a 4k block/sector size as backing for virtio. 512 byte request did work (thanks to host page cache) but a single 512 byte write might have triggered a 4k read and O_DIRECT accesses (avoiding host caching) was also not working. Testing and review is still in my todo list. Christian
