Re: [LI] Ext2 defrag

[Arun Sharma <adsharma@xxxxxxxxxxxxxxx>]

On Sun, Nov 21, 1999 at 11:29:42AM -0500, Shourya Sarcar wrote:

> Hi friends !
> Could we have some feed back on the amount of non-contiguity in
> your disks. I think I have a _very_high non cont .. 2.2 % AFAIK non
> contiguity is not reported if fsck finds a _clean_ disk (good for u)
> $ tail  -80 /var/log/boot.log | grep "fsck"

IIRC, ext2fs doesn't fragment the filesystem as much as other dumber fs'es
do. So you almost don't have to defragment it. I can't find a reference
to the above statement - but you can look around to find one.

Bottomline - you don't get much of a performance benefit by defragging 
the filesystem. 

> Another Q : i haven't found a way to fsck my root partition apart from the
> usual bootup check. oh yes, its finally got into my thickhead why
> unmounting the root fs is disallowed :) does the defrag utility ( i
> haven't used it) defrag your root partition, too ?

You do that by remounting the root partition read only (look in rc.sysinit).

Also, some related technical info - though all of your data is contiguous
on the disk, you may not get good performance if the contents of a 
particular directory is spread over a large number of cylinders.

This is one scenerio in which the BSD fs performs worse than ext2fs:

http://www.freebsd.org/cgi/getmsg.cgi?fetch=376787+382360+/usr/local/www/db/text/1998/freebsd-hackers/19980830.freebsd-hackers
http://docs.freebsd.org/cgi/getmsg.cgi?fetch=646048+0+archive/1998/freebsd-hackers/19980830.freebsd-hackers

	-Arun

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