Disk defragmenter in Linux

[Les Mikesell]

On Tue, 2006-01-03 at 02:35, Hans Kristian Rosbach wrote:
> > 
> > There's always backup/mkfs/restore.  If you aren't prepared
> > to restore you should probably take care of that before
> > worrying about efficiency.
> 
> Do you know how long time it would take to put back 800GB of
> mailboxes on our mailserver from the tape backup?
> No customers in the world would allow us to actually take
> such a time-off from serving their mail.

How do you plan to deal with an operator or software error
that erases your current files?

> Granted we COULD set up another box with a 1TB raid5 array
> to hold the data temporarily, but it would still take time
> since we would still have to shut down mail services before
> taking a copy. It would still be a bad workaround for a
> real problem. (Yes I know that ~99% of us don't ever need it)

You can do a swap like this with very little downtime if
you do an rsync while the system is live to get most of
the data copied, the repeat the rsync with the --delete
option to catch any subsequent changes with the system
offline, then swap mountpoints.  

> Thus we would need an on-line defragmenter that we could
> set up for a low-prio night run once or twice a year.

If you use maildir or other 1-message-per-file format,
a defragmenter isn't going to help much because it
won't know to move the directory contents together.
If you have standard mbox format you just have to
re-write them periodically which will happen anyway
if the users ever delete anything.

-- 
  Les Mikesell
   lesmikesell at gmail.com