Filesystem fragmentation and scatter-gather DMA

William Tambe tambewilliam at
Sun Mar 16 23:56:27 UTC 2008

Is the delay due to mechanical parts or the electronics gathering the fragments?

Would that same delay still apply to a solid state drive? Since a
solid state drive is really just a slower version of system memory
(Please correct me if I am wrong).

On Sun, Mar 16, 2008 at 5:29 PM, Andreas Dilger <adilger at> wrote:
> On Mar 16, 2008  15:13 -0500, William Tambe wrote:
> > When designing a filesystem, is fragmentation really an issue if
> > access to the disk can be done using scatter-gather DMA techics ?
> Yes!!!  Scatter-gather only handles "fragmentation" in memory, where
> seek time is zero.  If there is fragmentation on disk you pay 8ms
> for each fragment in the read.
> Cheers, Andreas
> --
> Andreas Dilger
> Sr. Staff Engineer, Lustre Group
> Sun Microsystems of Canada, Inc.

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