a type of RAID configuration. Involves two identical drives. In a mirrored set, all the data is duplicated to the two drives. If one fails, the other is instantly available. It is not faster than a single drive, but is probably not slower. An advantage of this is that in order to lose any of your data, the two drives would have to fail simultaneously. This is a good first-line of defense against losing all of your data. Caution: When setting up a mirror drive, MAKE SURE IT WORKS! Some people who set up a mirroring drive on their computer correctly find that it just doesn’t work. To check for this try turning off the computer and removing a drive and then turning it back on to see if the computer can switch to the other drive.