Lacie 4big Quadra White Paper - Page 7

LaCie RAID Technology White Paper RAID 0 RAID 1 RAID 3 RAID 3+Spare RAID 5 RAID 5+Spare RAID 6 RAID 0+1 RAID 10 Concatenation JBOD RAID Selection RAID 5+Spare RAID 5+Spare, is a RAID 5 array in which one disk is used as spare to rebuild the system as soon as a disk fails. At least four disks are required. If one physical disk fails, the data remains available because it is read from the parity blocks. Data from a failed disk is rebuilt onto the hot spare disk. When a failed disk is replaced, the replacement becomes the new hot spare. No data is lost in the case of a single disk failure, but if a second disk fails before the system can rebuild data to the hot spare, all data in the array will be lost. Applications The main advantage of RAID 5+Spare is that users can continue to access data even while the data is rebuilt to the spare drive. RAID 5+Spare has good data safety but disk space is limited by the presence of the hot spare which is not used until one of the other disks fails. 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. LaCie Products with RAID 5+Spare ✦✦ LaCie 4big quadra ✦✦ LaCie 5big network RAID 5+Spare A1 B1 Cp D1 Disk 1 A2 Bp C1 D2 Disk 2 Ap B2 C2 Dp Disk 3 Spare Disk 4 How RAID 5+Space Capacity Is Calculated Each disk in a RAID 5+Spare system should have the same capacity. Storage capacity in a RAID 5+Spare configuration is calculated by subtracting the number of drives by two and multiplying by the disk capacity, or C = (n-2)*d where: C = available capacity n = number of disks d = disk capacity For example, in a RAID 5+Spare array with four drives each with a capacity of 1000GB, the total capacity of the array would be 2000GB: C = (4-2)*1000 Page 7