3Ware 9550SX-4LP User Guide - Page 17

Understanding RAID Concepts and Levels RAID 1 Also known as a mirrored array. Mirroring is done on pairs of drives. Mirrored disk arrays write data to two drives using RAID 1 algorithms (see Figure 2). This gives your system fault tolerance by preserving the data on one drive if the other drive fails. Fault tolerance is a basic requirement for mission critical systems like web and database servers. 3ware uses a patented technology, TwinStor®, on RAID 1 arrays for improved performance during sequential read operations. With TwinStor technology, read performance is twice the speed of a single drive during sequential read operation. The adaptive algorithms in TwinStor technology boost performance by distinguishing between random and sequential read requests. For the sequential requests generated when accessing large files, both drives are used, with the heads simultaneously reading alternating sections of the file. For the smaller random transactions, the data is read from a single optimal drive head. Figure 2. RAID 1 Configuration Example RAID 5 Combines striping data with parity (exclusive OR) to restore data in case of a drive failure. This array type provides performance, fault tolerance, high capacity, and storage efficiency. Requires a minimum of three drives. Parity information is distributed across all drives rather than being concentrated on a single disk (see Figure 3). This avoids throughput loss due to contention for the parity drive. RAID 5 0 parity A1 A2 A3 A4 A Blocks B0 1 parity B2 B3 B4 B Blocks C0 C1 2 parity C3 C4 C Blocks D0 D1 D2 3 parity D4 D Blocks E0 E1 E2 E3 4 parity E Blocks Figure 3. RAID 5 Configuration Example www.3ware.com 7