Occasionally, a file system becomes so damaged that you must completely restore it. Typically, you need to restore a complete file system after a disk head crash. You might need to replace the hardware before you can restore the software. See Chapter 30, SPARC: Adding a Disk (Tasks) or Chapter 31, IA: Adding a Disk (Tasks) for information on how to replace a disk. Fully restoring a file system such as /export/home can take a lot of time. If you have consistently backed up file systems, you can restore them to their state from the time of the last incremental backup.