DiskWarrior 2.1 is a Mac OS 7.1 to Mac OS 9 application that is compatible with Mac OS X Extended disks, and even repairs problems found only on this type of disk. It also repairs disks containing both Mac OS 9 and Mac OS X. In order to rebuild any disk (including your Mac OS X startup disk), you must start your computer from a Mac OS 9.x disk, such as the DiskWarrior 2.1 CD. If you do not have a DiskWarrior 2.1 CD, Chris Breen of Macworld.com has a movie about how to burn an emergency boot CD.
DiskWarrior 2.1 is not compatible with disks that have Mac OS X 10.4 (Tiger) or later installed. It is also not compatible with any disk that has been attached to a Mac running Mac OS X 10.4 or later.
For those disks with Mac OS X 10.2.2 to 10.3.9 installed and journaling turned on, DiskWarrior 2.1 will rebuild the directory of the disk, but it will turn off journaling. Once DiskWarrior 2.1 has finished rebuilding the directory, you will need to turn journaling back on. This is not an issue for DiskWarrior 3.0 and later.
When run under Mac OS X's Classic environment, DiskWarrior 2.1 will not be able to rebuild the directories of any disks. Once again, in order to rebuild any disk you must start your computer from a Mac OS 9.x disk such as the DiskWarrior 2.1 CD. DiskWarrior will not rebuild UFS disks. The DiskWarrior 2.1 Extension will load in Mac OS X's Classic environment, but it will not protect any disks.