On Mar 12, 2007 10:26 -0400, Jeff Garzik wrote: > In my own experiments on my own Fedora workstation, ~66% of IOs in Linux > start on an odd sector, and ~33% started on even-numbered sectors. For > a 1K-sector drive with 'odd' alignment, the configuration Microsoft will > likely want, that means the majority of disk transactions will avoid a > RMW cycle, but a still-numerous minority will not. Isn't that purely an artifact of the DOS partition table alignment, possibly skewed by the fact that most of your IO is on partition 1 & 3? Hard to believe this because of the nice even numbers though. Since ext3 has at least 1kB blocksize and defaults to 4kB blocksize with most modern disks because they are > 500MB in size, you should never have misaligned writes generated by the filesystem itself. > I did not test > transfer length, to see how many transfers /ended/ on an odd sector, > thus determining how many RMW cycles the tail of an average I/O requires. I'd guess a vast majority of IO will have the end similarly misaligned as the start. Very little filesystem IO is 512 bytes, possibly excluding XFS in an unusual mode. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
