System Administration Guide, Volume 1

SPARC: About System and Secondary Disks

A system disk contains the root (/) or /usr file systems, or both. If the disk containing either of these file systems becomes damaged, you have two ways to recover:

A secondary disk doesn't contain the root (/) and /usr file systems. It usually contains space for user files. You can add a secondary disk to a system for more disk space or you can replace a damaged secondary disk. If you replace a secondary disk on a system, you can restore the old disk's data on the new disk.