Lacie 4big Quadra User Manual - Page 16

LaCie 4big Quadra Enterprise Class • Design by Neil Poulton User Manual RAID page 16 3.1.4. RAID 3 and RAID 3+Spare RAID 3 uses byte-level striping with a dedicated parity disk (Disk 4 in Fig. 10 and Fig. 11) so that one volume mounts on the computer. A RAID 3 array can tolerate a single disk failure without data loss. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. If a second disk fails before data can be rebuilt to a replacement drive, all data in the array will be lost. In RAID 3+Spare, one disk in the array is left empty. If a drive in the array fails, the data from the failed disk is automatically rebuilt to the empty or "spare" disk (Fig. 11). Applications RAID 3 provides good data safety for environments where long, sequential files are being read, such as video files. Disk failure does not result in a service interruption because data is read from parity blocks. RAID 3 is useful for people who need performance and constant access to their data, like video editors. RAID 3 is not recommended for intensive use with nonsequential files because random read performance is hampered by the dedicated parity disk In RAID 3+Spare disk failure does not require immediate attention because the system rebuilds itself using the hot spare, but the failed disk should be replaced as soon as possible. RAID 3 A1 A4 B1 B4 C1 C4 Disk 1 Fig. 10 A2 A5 B2 B5 C2 C5 Disk 2 A3 A6 B3 B6 C3 C6 Disk 3 Ap(1-3) Ap(4-6) Bp(1-3) Bp(4-6) Cp(1-3) Cp(4-6) Disk 4 RAID 3+ Spare A1 A3 B1 B3 C1 C3 Disk 1 Fig. 11 A2 A3 B2 B4 C2 C4 Disk 2 Ap(1-2) Ap(3-4) Bp(1-2) Bp(3-4) Cp(1-2) Cp(3-4) Disk 3 Spare Disk 4