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

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

On Fri, 22 Aug 2008, Szabolcs Szakacsits wrote:
> 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

Retested with a different disk, SATA-II, NCQ, capable of 70-110 MB/s 
read/write:

                               MB/s    Runtime (s)
                              -----    -----------
  btrfs unstable, no dup      51.42        168
  btrfs unstable              42.67        197
  ext4 2.6.26                 35.63        245
  nilfs2 2nd+ runs            26.43        287
  ntfs-3g unstable            21.41        370
  ext3                        19.92        559
  xfs nobarrier               14.17        562
  reiserfs                    13.11        595
  nilfs2 1st run              12.06       3719
  xfs nobarrier, ncq, wc off   6.89       1070
  xfs                          1.95       3786

	Szaka

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