Luckily my data needs for my server still fit on a single disk (500GB data, 500GB of backups from other machines).

So for me, I just throw disks at the problem. I stick with a 3 disk RAID1 array, which means I can take any single drive out at any point and still have redundancy. And any drive I take out can be used to rebuild the full setup.

I'm planning on moving to XFS soon, I'll still be sticking with mirroring though (probably a 4 disk mirror now). I'll probably add an SSD as a cache device too, given that I have a 160GB doing nothing at the moment.

XFS seems to be so much more robust that most other file systems.

mhddfs sounds interesting though, but I'm glad I don't need it