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

[Szabolcs Szakacsits <szaka@ntfs-3g.org>]

On Fri, 22 Aug 2008, Dave Chinner wrote:
> On Thu, Aug 21, 2008 at 08:33:50PM +0300, Szabolcs Szakacsits wrote:
>
> > 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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