Why partition disks?

[Flint Pellett]

Reasons for having more than one file system:

1. Each file system can have at most 65,535 inodes, because the inode
number is stored in a 16 bit field in the directories.  That means you
have a maximum of that many files in the file system-- which may sound
like a lot until you look at that 1.2 GB space and realize that if your
average file is less than about 18K bytes you'll run out of inodes
long before you are able to take advantage of the disk space.  Keeping
news in it's own file system (since it tends to use up lots and lots
of inodes) is often a good idea.

2. If you have any users you don't completely trust - (perhaps because
they are still naive and don't know what they are doing, not necessarily
because they are dishonest) you can restrict them to one file system,
but if there is only one file system then they may do something wrong
and use up all the space everywhere, which could then cause other
things that aren't theirs to bomb off with no space in /tmp, etc.
(Don't laugh- it happens.  I had a group of 3 college level users
end up copying all of /usr into the home directories of new logins
they were creating in /usr2 when they screwed up their creation script.
(They were copying /usr/$TEMPLATE to the new location when $TEMPLATE
was not set, or something like that.)  I first found out about it
when they complained that "Creating logins used to take 10 seconds
and now it takes 20 minutes per login...")

3. You need to think about how you are going to do backups.  If you have
a tape unit that handles 1.2GB/tape maybe this doesn't matter, or if you
have backup software better than the usual default of a cpio to the
tape it may not matter.  But if you are copying onto 150MB tapes with
the normal backup scripts that cpio one filesystem at a time to a series
of tapes it does matter- having to recover a single file that someone
accidentally deletes from the 7th tape of an 8 tape cpio archive will be
pretty painful and slow.  If you created 4 partitions of 300MB each,
then each backup will use at most 2 tapes;  recovering a file becomes
a lot less of a chore, because you won't have to hunt through more
than 2 tapes to find it.  This also makes the backups more "secure":
if tape 2 of your 8 tape backup is unreadable because Sally Operator
spilled Pepsi on it, only part of your backup becomes unuseable, not
all of it.
-- 
Flint Pellett, Global Information Systems Technology, Inc.
1800 Woodfield Drive, Savoy, IL  61874     (217) 352-1165
INTERNET: flint%gistdev at uxc.cso.uiuc.edu
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