EMC CX500I Configuration Guide - Page 35

RAID Types and Trade-offs Stripe Element Size Stripe Blocks First Disk 0-127 512-639 1024-11511536-1663 Parity ... Second Disk 128-255 640-767 1152-1279 Parity 2048-2175 ... Stripe Size Third Disk 256-383 768-895 Parity 1664-1791 2176-2303 ... 384-511 Fourth Disk Parity 1280-1407 1792-1919 2304-2431 ... Parity Fifth Disk 896-1023 1408-1535 1920-2047 2432-2559 ... User Data Parity Data EMC1815 Figure 2-2 RAID 5 Group RAID 5 Groups offer excellent read performance and good write performance. Write performance benefits greatly from storage-system caching. RAID 3 Group (Parallel Access Array) A RAID 3 Group consists of five or nine disks. The hardware always reads from or writes to all the disks. A RAID 3 Group uses disk striping. Limit concurrent access to RAID 3 LUNs for the best bandwidth performance. For example, A RAID 3 Group may have multiple LUNs, but the highest bandwidth is achieved with 1 to 4 threads of concurrent, large I/O. The storage system writes parity information that lets the Group continue operating if a disk fails. When you replace the failed disk, the SP rebuilds the group using the information stored on the working disks. Performance is degraded while the SP rebuilds the group. However, the storage system continues to function and gives users access to all data, including data stored on the failed disk. RAID Types 2-5