Which Linux filesystem is best for a huge Apache mod_disk_cache partition

Attempting to expand on @Zoredache's answer, as I give this a go myself:

• Create a new group (www-pub) and add the users to that group

  groupadd www-pub

  usermod -a -G www-pub usera ## must use -a to append to existing groups

  usermod -a -G www-pub userb

  groups usera ## display groups for user

• Change the ownership of everything under /var/www to root:www-pub

  chown -R root:www-pub /var/www ## -R for recursive

• Change the permissions of all the folders to 2775

  chmod 2775 /var/www ## 2=set group id, 7=rwx for owner (root), 7=rwx for group (www-pub), 5=rx for world (including apache www-data user)

  Set group ID (SETGID) bit (2) causes the group (www-pub) to be copied to all new files/folders created in that folder. Other options are SETUID (4) to copy the user id, and STICKY (1) which I think lets only the owner delete files.

  There's a -R recursive option, but that won't discriminate between files and folders, so you have to use find, like so:

  find /var/www -type d -exec chmod 2775 {} +

• Change all the files to 0664

  find /var/www -type f -exec chmod 0664 {} +

• Change the umask for your users to 0002

  The umask controls the default file creation permissions, 0002 means files will have 664 and directories 775. Setting this (by editing the umask line at the bottom of /etc/profile in my case) means files created by one user will be writable by other users in the www-group without needing to chmod them.

Test all this by creating a file and directory and verifying the owner, group and permissions with ls -l.

Note: You'll need to logout/in for changes to your groups to take effect!

How much do you value the data?

Seriously, each filesystem has its own tradeoffs. Before I go much further, I am a big fan of XFS and Reiser both, although I often run Ext3. So there isn't a real filesystem bias at work here, just letting you know...

If the filesystem is little more than a container for you, then go with whatever provides you with the best access times.

If the data is of any significant value, you will want to avoid XFS. Why? Because if it can't recover a portion of a file that is journaled it will zero out the blocks and make the data un-recoverable. This issue is fixed in Linux Kernel 2.6.22.

ReiserFS is a great filesystem, provided that it never crashes hard. The journal recovery works fine, but if for some reason you loose your parition info, or the core blocks of the filesystem are blown away, you may have a quandry if there are multiple ReiserFS partitions on a disk - because the recovery mechanism basically scans the entire disk, sector by sector, looking for what it "thinks" is the start of the filesystem. If you have three partitions with ReiserFS but only one is blown, you can imagine the chaos this will cause as the recovery process stitches together a Frankenstein mess from the other two systems...

Ext3 is "slow", in a "I have 32,000 files and it takes time to find them all running ls" kinda way. If you're going to have thousands of small temporary tables everywhere, you will have a wee bit of grief. Newer versions now include an index option that dramatically cuts down the directory traversal but it can still be painful.

I've never used JFS. I can only comment that every review of it I've ever read has been something along the lines of "solid, but not the fastest kid on the block". It may merit investigation.

Enough of the Cons, let's look at the Pros:

XFS:

• screams with enormous files, fast recovery time
• very fast directory search
• Primitives for freezing and unfreezing the filesystem for dumping

ReiserFS:

• Highly optimal small-file access
• Packs several small files into same blocks, conserving filesystem space
• fast recovery, rivals XFS recovery times

Ext3:

• Tried and true, based on well-tested Ext2 code
• Lots of tools around to work with it
• Can be re-mounted as Ext2 in a pinch for recovery
• Can be both shrunk and expanded (other filesystems can only be expanded)
• Newest versions can be expanded "live" (if you're that daring)

So you see, each has its own quirks. The question is, which is the least quirky for you?