Recovering data from a failed RAID can easily turn into a costly ordeal. Please read this chapter carefully before proceeding. If you would like to get help from experts, please consider using our fee-based RAID recovery services. See "Chapter 20: RAID Recovery Services."

First determine whether the RAID is hardware-based or software-based. The recovery procedures are very different.

RAID

A RAID is the organization of multiple disks into a larger logical disk for better performance and/or availability. There are many levels of RAID; we will discuss levels 0 and 5.

In RAID 0 (or striped volume) data is striped across all disks in a rotating pattern. A RAID 0 with two 20-GB disks will function as one 40-GB logical disk with no redundancy. If any disk fails, data is lost.

In RAID 5 data is also striped across all disks in a rotating pattern but with parity data for redundancy. A RAID 5 with three 20-GB disks will function as one 40-GB logical disk. Parity information uses up the equivalence of one disk.

A RAID 5 becomes degraded when one disk fails. The RAID, however, still functions because the data on the failed disk can be computed using the parity information and data on the remaining disks.