sotware raid - don't forget to update your initramfs!
Just a quick tip to avoid a problem I just encountered. Yesterday I'd added a new drive to my software raid array but forgot to update the initramfs. While this isn't a problem for RAID 1, it probably is for most other RAID levels.
The end result was I could boot but not mount the root file system because Linux didn't seem to know about the extra drive. I'm running Debian so I got dropped into a busybox that didn't quite have enough features (namely no ability to create a mount point for my arrays) to resolve the problem.
I ended up downloading a Debian NetInst disk and using it in rescue mode. After starting my RAID arrays, I mounted and chrooted to the root array, mounted the /boot RAID 1 partition and updated the initramfs.