Hot Spares
Hot spares are one of the greatest friends of any sysadmin. They let me sleep at night knowing that if a harddrive explodes in a RAID array, nothing too bad will happen. The hot spare will take over for the failed drive and the array will not degrade. Then I can come in the next day, swap out the dead drive, and watch the hot spare copy over to the new drive. Use them, love them, get some sleep.
