Re: XFS vs Elevators (was Re: [PATCH RFC] nilfs2: continuous snapshotting file system)

On Fri, 22 Aug 2008, Dave Chinner wrote:

On Thu, Aug 21, 2008 at 08:33:50PM +0300, Szabolcs Szakacsits wrote:

quoted

The 'nobarrier' mount option made a big improvement:

INteresting. Barriers make only a little difference on my laptop;
10-20% slower. But yes, barriers will have this effect on XFS.

If you've got NCQ, then you'd do better to turn off write caching
on the drive, turn off barriers and use NCQ to give you back the
performance that the write cache used to. That is, of course,
assuming the NCQ implementation doesn't suck....

Write cache off, nobarrier and AHCI NCQ lowered the XFS result:

                               MB/s    Runtime (s)
                              -----    -----------
  btrfs unstable              17.09        572
  ext3                        13.24        877
  btrfs 0.16                  12.33        793
  ntfs-3g unstable            11.52        673
  nilfs2 2nd+ runs            11.29        674
  reiserfs                     8.38        966
  xfs nobarrier                7.89        949
  nilfs2 1st run               4.95       3800
  xfs nobarrier, ncq, wc off   3.81       1973
  xfs                          1.88       3901

	Szaka

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