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Re: [Q] Is this true and does it mean there is dynamic entation in ext2/3?



[Resurrecting an ancient thread...]

On Tue, 21 Jun 2005, Markus Peuhkuri wrote:
Theodore Ts'o wrote:

Ext2/3 has advanced algorithms to make sure that the blocks that are
allocated avoid fragmentation, but it is not doing any kind of dynamic

And there is a tool 'filefrag' in e2fsprogs that reports how fragmented
a particular file is.  If your disk grows full (over 90-95%, depending
on file sizes etc..) then it is more difficult to find continuous blocks
for files.  Now, if you delete files, then new files most probably are
non-fragmented but those files that were written when disk was full are
still fragmented.

You can "unfragment" those files just by copying them and deleting old
ones (if you have plenty of free space), but as Damian told, you must be
careful with locks and nfs handles.

I have a user who is complaining of general slowness on his machine (RH9, so e2fsprogs-1.32-6). The slowness is particularly bad when he types "mail" to read his email. I can't find anything wrong with the system itself (no cpu load, free ram, no heavy disk activity, etc) but did note that when opening his mailbox (only 26M, so nothing huge) it does hang for 5-10 secs, apparently waiting on disk. Running filefrag on his mailbox indicates it has 1119 extents. I suspect that may be the source of the problem.


Now, I realize some fragmentation is normal, but I'd have expected that a mailbox with 328 messages wouldn't get more than 328 fragments (or possibly twice that many) maximum. And the filesystem is only 42% full, so that's not causing extra fragmentation.

Is there anything I should be watching for here, or should I just give up and copy the file?

Damian Menscher
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