Re: [Jfs-discussion] Fragmentation and poor write speeds.

[Jason F. <jas...@gm...>]

I'm at 99% right now (30GB free) -- I'll free some space, test again every
5% and report back.

Interestingly, a dd if=/dev/zero of=fragtest bs=40k count=1;filefrag
fragtest results in that file using 3 extents instead of 1 roughly every
10th-11th creation.

Just for reference, a fresh JFS on the same 7-disk RAID5/LVM partition gets
185MB/sec writes consistently.

Thanks for the help,
Jason

On 1/19/07, Dave Kleikamp <sh...@li...> wrote:
>
> On Fri, 2007-01-19 at 01:38 -0500, Jason Fisher wrote:
> > I have a 1.6TB jfs partition (Linux) that is roughly a year old.  In
> > this time, the write speed has managed to drop to 5MB/sec and it has
> > become nearly unusable.  I mainly use the RAID for mythtv, but
> > recently it has become too slow for capturing.
> >
> > filefrag reports some 3GB files with 90,000 extents next to 3GB files
> > with 18 extents.  Many files with thousands of extents.
> >
> > I understand there are no defrag tools available for Linux, and I
> > would rather not back the data up and restore as it's important, but
> > just not important enough to warrant the time spent.
> >
> > Is there another way I can deal with these files?
> >
> > I copied a file with 3000 extents off the partition and onto a spare,
> > deleted the original and copied the file back and ended up with 1100
> > extents.  An improvement, but would this method ever get performance
> > back to a usable level?
>
> I'm not sure if this will make much of a difference.  Defragging the
> existing files one at a time may not have much of an effect on the
> remaining free space, so a new file being captured may be just as
> fragmented as before.
>
> > What if I were to fill the remaining space
> > with dd after deleting the original/before copying it back?
>
> I don't think this will do anything useful.
>
> > Or should
> > I concentrate on freeing up as much space as possible before copying
> > any files to/from?
>
> The more free space you have, the better.  I don't know how close to
> full your disk is, but you may want to try to maintain a certain amount
> of free space and see how that affects performance.  If you do find a
> "sweet spot" such as having good performance when the disk is say 80%
> full, I'd be interested to know that.  Hopefully that percentage isn't
> too low.
>
> > Thanks,
> > Jason
> --
> David Kleikamp
> IBM Linux Technology Center
>
>