Ext3 users - Dec 2005 - Repacking files on ext3?

I found this thread from a few months ago that seems to have been 
started by someone with the same problem I have, but it was not resolved:

https://www.redhat.com/archives/ext3-users/2005-March/msg00000.html

I have been trying to speed up my boot times and I notice that a lot of 
time is spent waiting on IO.  Even with readahead-list precacheing 
files, it is reading at less than 1/4 of my disk's maximum sequential 
throughput.  I feel this is because the files are scattered all around 
the disk, which causes a lot of seeking.

I am looking for a way to defragment the disk such that the files needed 
for boot are all packed sequentially at the beginning of the disk, so 
that readahead-list can read them in much faster.

During that previous thread, it was stated that it was impossible to 
have defrag work safely on an ext3 partition.  I do not see why this is 
so.  If ext2 could be given a journal to make it crash resistant, then 
why can't defrag be given the same thing?

Another comment was made saying that such a defragger could not possibly 
be done only in userspace.  Unless you're talking about online 
defragmentation, then manipulating the filesystem offline to repack it 
is entirely possible from userspace.

Is there still no way to do what I am trying?

P.S. Please CC me on replies, as I am not subscribed.

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Phillip Susi schrieb:
> I am looking for a way to defragment the disk such that the files needed
> for boot are all packed sequentially at the beginning of the disk, so
> that readahead-list can read them in much faster.
i've never used ext2fs defrag-programs so i don't know how
"safe" they
are. but if they're working on ext2 - why not tune2fs' an existing ext3
into a ext2, run the defrag program and tune2fs' into ext3 again:

% umount /dev/sdX
% tune2fs -O ^has_journal /dev/sdX
% <run magic defrag program on sdX>
% tune2fs -O has_journal /dev/sdX
% mount /dev/sdX

obviously this has to be done while the device is offline and i'd
recommend having backups of course. i've never tried it though...
- --
BOFH excuse #86:

Runt packets
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