On Tue, Oct 29, 2013 at 8:51 AM, Anand Avati <avati at gluster.org> wrote: > Looks like what is happening is that qemu performs ioctls() on the backend > to query logical_block_size (for direct IO alignment). That works on XFS, > but fails on FUSE (hence qemu ends up performing IO with default 512 > alignment rather than 4k). > > Looks like this might be something we can enhance gluster driver in qemu. > Note that glusterfs does not have an ioctl() FOP, but we could probably wire > up a virtual xattr call for this purpose. > > Copying Bharata to check if he has other solutions in mind. Hi Avati and Bharata, QEMU's 4 KB sector status is as follows: QEMU does not autodetect sector size but you can tell the guest by setting -drive logical_block_size=,physical_block_size=,min_io_size= properties on the QEMU command-line. I'm not aware of an XFS sector size ioctl() probe that you mentioned. Note that QEMU can issue disk I/O internally when starting up (to detect the image file format) or to access image format metadata (qcow2, qed, etc). This is usually not a problem if you explicitly set -drive format=<format> on the command-line to skip file format probe. qcow2 operates on 64 KB clusters by default so 4 KB disks work. Finally, the BIOS running inside the guest is not 4 KB sector-aware. Therefore, 4 KB sector disks can be used as data disks but attempting to boot from them will hit I/O errors. I'm happy to help if you want to discuss improvements and integration with GlusterFS. Stefan
