Filesystem fragmentation and scatter-gather DMA

Andreas Dilger adilger at
Sun Mar 16 22:29:03 UTC 2008

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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