resizing partitions in the same slice

[Matthew Seaman]

On Fri, Mar 12, 2004 at 05:02:10PM -0600, Eugene Lee wrote:
 
> I'm a little surprised.  I would think that resizing partitions is a
> common request, that the idea of growing one partition while shrinking
> another is not a new or rare notion.  Can anyone else share their views
> or experiences?  The list archives contain few comments on the subject.

Absolutely.  This is something that there is a great deal of pent up
demand for.  Consequently growfs(8) exists, which can extend a
filesystem.  Normally growfs(8) is used in a RAID environment, where
extra space can be added to a slice relatively easily.  However, it
can certainly be used on a regular harddrive.  You'll need to re-do
the partitioning as a separate job, and be very careful about the
whole job, as a misstep will possibly trash the whole disk.

While growfs(8) does it's job very well, there's some obvious areas
where it's functionality could be extended.  The first would be a
mechanism for being able to run growfs on a mounted filesystem.
That's hugely important for fileservers with very large filesystems
and hundreds of network clients.  Models for how to do this already
exist: for instance see the lockfs(1M) implementation from Solaris:

    http://www.freebsd.org/cgi/man.cgi?query=lockfs&apropos=0&sektion=0&manpath=SunOS+5.9&format=html

The other obvious extension is 'shrinkfs' which at the moment can only
be achieved by backing up the partition and restoring it into a
smaller space.  The problem with shrinkfs is that it requires shifting
the on-disk data into a smaller region, something which is
intrinsically much more difficult than just providing an extra chunk
of empty space.  As far as I know, no one has yet managed to produce a
working shrinkfs implementation under any sort of Unix or Unix derived
system.

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP: http://www.infracaninophile.co.uk/pgpkey         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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