Backing up and protection come to mind as well.  The /usr directory can 
most likely be mounted as read-only in most instances.  Once the system is 
stable, switch /usr to read-only and make a backup of it.  You'll only need 
another backup of it if you ever switch it out of read-only.  Not that I've 
done this yet but it's on my list of things to do.....

At 09:19 AM 6/29/2001 -0400, Nate Johnston wrote:
>Scott Horton spake thus: (Thu, Jun 28, 2001 at 10:43:10PM -0500)
>
> > So - my question - in a single-disk system, why this longstanding tradition
> > of breaking the filesystem up into multiple partitions?  (There!  I've
> > unveiled my ignorance of *nix filesystems in general!)
>
>First, there is no reason requiring this kind of a split.  I have seen
>plenty of systems, particularly desktops, that have one gigantic /, and
>the only other filesystem is swap.  While this is generally considered
>Bad Form it is ok for a desktop.
>
>Second, Unix has its roots in multi-disk server systems.  Your laptop
>running NetBSD thinks more like a Sun Starfile E10000 than the same
>laptop running Windows.  So, when I as a system administrator administer
>large produciton unix systems I configure my desktop unices to be
>similar.  Given the roots NetBSD has in old unix, and people like me who
>have a utilitarian reason to make their laptops look vaguely like their
>servers, more people accept multi-filesystem setups as the norm.
>
>Third, it increases functionality through modularity.  I have to keep my
>work data separate from other data as a corporate requirement, therefore
>when I go into work I use a different /home partition on my laptop than
>when I am at home (using the automounter).  Since filesystems are a
>relatively static part of the system this doesn't usually come up much
>but it is there.
>
>Lastly, having multiple filesystems localizes errors.  If there is a
>physical disk error, chances are that it is unlikely to be in the small
>center track that contains my root and other boot-critical filesystems.
>It is likely to be on an exterior track, where my /home, /export, or
>/usr live.  The same process works for localizing application level
>errors; here is an excerpt I got from a general google search "why does
>unix use separate filesystems".  It is representative of the philosophy
>and the mentality.
>
>from http://www.aplawrence.com/Boot/filesystems.html
>
>"You want to control how much data gets put on a drive. For example, in
>some environments, I'll make /var/spool/lp/temp a small filesystem of
>its own. This causes it to fill up if there are too many unfulfilled
>print jobs, which calls attention to the problem before it really gets
>out of hand and fills up something more important. The idea here is that
>it's better not to print than not to work at all."
>
>--N.
>
>--
>Nate Johnston                           nmj3e@alumni.virginia.edu
>GPG footprint: DEAF B505 0D84 1AEF A43F  91C5 71B3 D053 D0E1 3C05
>Unix System Administrator               SingleSignon.net