On 11/26/11 7:06 PM, Dave Chinner wrote: > On Thu, Nov 24, 2011 at 05:50:42PM -0200, Carlos Maiolino wrote: >> On Thu, Nov 24, 2011 at 05:20:51PM -0200, Carlos Maiolino wrote: >>> xfsprogs (mainly mkfs) is using the logical sector size of a volume to initialize >>> the filesystem, which, even in devices using Advanced Format, it can get a 512 >>> bytes sector size if it is set as the logical sector size. >>> This patch changes the ioctl to get the physical sector size, independent of the >>> logical size. >>> >> >> Just as information, this patch proposal does not change the behaviour of mkfs in case the >> user is using libblkid, which in case, mkfs will take advantage of libblkid to retrieve disk >> topology and information. >> I'm not sure if libblkid is the best way to retrieve the device sector's size here, since >> this does not provide a way to retrive the physical sector size, only the logical size, but >> I can be very wrong. > > If libblkid exports the PBS (physical block size) as exposed in > /sys/block/<dev>/queue/physical_block_size, then we should be able > to get it. > > However, the issue in my mind is not whether it is supported, but > what is the effect of making this change? The filesystem relies on > the fact that the minimum guaranteed unit of atomic IO is a sector, > not the PBS of the underlying disk. What guarantees do we have when > do a PBS sized IO is doesn't get torn into sector sized IOs by the > drive and hence only partitially completed on failure? Indeed, if > the filesystem is sector unaligned, it is -guaranteed- to have PBS > sized IOs torn apart by the hardware.... > > i.e. do we have any guarantee at all that a PBS sized IO will either > wholly complete or wholly fail when PBS != sector size? And if not, > why is this a change we should make given it appears to me to > violate a fundamental assumption of the filesystem design? I had the expectation that physical block size WAS the fundamental/atomic IO size for the disk, and anything smaller required read/modify/write. So I made this suggestion (and I think hch concurred) so that we weren't doing log IOs which required RMW & translation. i.e. for a 4k physical / 512 logical disk - wouldn't we want to choose 4k sectors? Ok, if we have mismanaged the alignment and aligned to logical, not physical, then I guess there would be an issue... but at that point we've already messed up (though not catastrophically I guess)... -Eric > Cheers, > > Dave. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
