I built a fileserver from parts this weekend and installed three 250GB IDE drives which I have now configured into a raid 5 setup. I formatted the array into an ext2 filesystem because that was the example that was given in the Software-RAID-HOWTO (the command is: mke2fs -b 4096 -R stride=8 /dev/md0).

But I was wondering, can you use a journaling filesystem on a RAID array? Does it make any sense to?

The system you pick should be based more on the type of files you have. You can use anyone you want.

ReiserFS4 is probably the fastest filesystem. Reiser4, last I heard, still isn't fully supported yet though, so you might wana wait. I've seen some people having some problems, but not alot.

Reiser3 is nice, I used it for awhile. Not real sure about it other than its alot faster than Ext2 and Ext3 are.

XFS is best one for large amounts of large files, I personally use XFS on my desktop and I don't have any large files, except for a crap load of pictures, and it loads all of those up really fast.

I haven't heard anything about JFS yet, but I'm still waiting.

Absolutely yes! You really should use a journaling fs. fsck'ing after a crash will take a very long time on a large array. Since you've already settled on ext2 going with ext3 is probably easiest since you can do that without recreating the filesystem. Just unmount it, tune2fs -j /dev/md0, change fstab entry to ext3. Remount. Done.

I used xfs for my raid (4x320GB raid-5) because it mainly holds large files.

ext3 filesystem:
dirac:/raid # dd if=/dev/zero of=./test bs=1024k count=2048
86154529 bytes/s

dirac:/raid # dd if=./test of=/dev/null bs=1024k count=2048
174263984 bytes/s

write performance: 82.2MB/s
read performance: 166.2MB/s

xfs filesystem:
dirac:/raid # dd if=/dev/zero of=./test bs=1024k count=2048
185052817 bytes/s

dirac:/raid # dd if=./test of=/dev/null bs=1024k count=2048
180374561 bytes/s

write performance: 176.5MB/s
read performance: 172.0MB/s

These tests were done on a completely empty filesystem, and have little to do with real world throughput. However, the clients connect to this server via gigabit ethernet and the bottleneck is the network and not the disk i/o.

I expect the array will hold files of varying lengths. It will have all my pictures on it and my MP3 collection, and those are fairly large files (couple of MB apiece). But, it will also be used to back up two separate /home directories and three Windows boxes. The /home directories particularly will have a goodly collection of small configuration and setting files in them.

I don't have anything on the array yet (one of the drives seems to be giving some problems), so I could potentially reformat it though. Thank you both for your input. I'm going to take a look at the man pages for mkfs.ext3, mkreiserfs and mkfs.xfs and see if they tip me on one direction or the other.