Disk defragmenter in Linux

Ed Hill ed at eh3.com
Fri Dec 30 17:56:11 UTC 2005

On Fri, 2005-12-30 at 10:10 -0600, Mike McCarty wrote:
> Again, the point was that some claim that ext3 does not and will
> not fragment files which are not dynamic. I claimed that fragmentation
> can occur simply due to install of software, which some claimed
> will not and does not occur with ext3. I think that I have demonstrated
> my point. In fact, I was quite shocked that it was as bad as that,
> frankly.

Hi Mike,

OK, fragmentation can and sometimes does occur.  You've explained why
and how.

So the next logical question is: what difference, if any, does it make?
Can you or anyone else come up with a way to measure the effect or some
aspect of it?  Perhaps a benchmark that shows how application startup
times suffer?

I'm not a filesystems guru, but even so its not at all clear to me that
fragmentation must necessarily cause a big or repeated performance hit.
Given Linux's VM, it seems plausible that an initial file load might
suffer (maybe a lot or maybe a tiny bit?) and that subsequent file
accesses will be from pages already cached in RAM.  

We should all keep open minds and, if possible, generate some actual
benchmark data!


Edward H. Hill III, PhD
office:  MIT Dept. of EAPS;  Rm 54-1424;  77 Massachusetts Ave.
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