Ext3 and many other popular filesystems allow per-user and per-group quota. In some cases, a "per directory tree quota" is needed: doesn't matter who writes the files, limit a directory tree from growing to a size of more than X bytes.
As I see it, it can be good for many cases, either limiting a directory from exploding (Lior wrote about a similar problem a few weeks ago), or simply allocating space per team-projects on a file server.
As far as I knew, the only UNIX FS that implemented this feature was Sun's unpopular SAMFS/QFS. However, I've just stumbled upon this man page and was surprised to find out that the good old (well, at least old 🙂 ) XFS does that already!
A quick "howto use project quota" cookbook:
1. Make the filesystem and mount it:
> mkfs.xfs /dev/loop0
> mount /dev/loop0 /mnt/tmp -o pquota
2. Create a project named "project1", which is the "/mnt/tmp/tree1" tree:
> echo "11:/mnt/tmp/tree1" >> /etc/projects
> echo "project1:11" >> /etc/projid
> xfs_quota -x -c 'project -s project1' /mnt/tmp
3. Set the tree quota to 2 MB:
> xfs_quota -x -c 'limit -p bhard=2m project1' /mnt/tmp
4. That's it.. Now let's make some tests:
> dd if=/dev/zero of=/mnt/tmp/tree1/aaa count=10 bs=1024k
dd: writing `aaa': No space left on device
2+0 records in
1+0 records out2093056 bytes (2.1 MB) copied, 1.51164 s, 1.4 MB/s
> touch fdsa
touch: cannot touch `fdsa': Disk quota exceeded
5. And there's also a nice report! (looks nicer with a fixed-width console font)
> xfs_quota -x -c 'report /mnt/tmp'
Project quota on /mnt/tmp (/dev/loop0)
Blocks
Project ID      Used      Soft      Hard   Warn/Grace
---------- --------------------------------------------------
project1        2044         0      2048    00 [--------]
project2           0         0         0    00 [--------]