HP LH4r Installation and configuration of the HP NetRAID, NetRAID-1 and NetRAI - Page 26

Chapter 2 RAID Overview RAID 3: Striping with Dedicated Parity In RAID 3 configurations, each data stripe generates one parity block to provide redundancy and data protection. The parity block is encoded information that can be used to reconstruct the data on that stripe if one of the disks fails. RAID 3 configurations dedicate one disk in the array to store all parity blocks. If you have five physical drives configured as one RAID 3 logical drive, data blocks are written as follows: Disk 1 Disk 2 Disk 3 Disk 4 Disk 5 Stripe 1 Stripe 2 Stripe 3 Block 1 Block 5 Block 9 Block 2 Block 6 Block 10 Block 3 Block 7 Block 11 Block 4 Block 8 Block 12 Parity 1-4 Parity 5-8 Parity 9-12 With RAID 3, data reads are faster than writes, because parity must be calculated for writes. RAID 3 performs better for long writes than for short ones, because writes of less than one full stripe involve a parity calculation. RAID 3 works well for long data transfers, such as CAD files and data logging. RAID 3 Advantages There is no data loss or system interruption due to disk failure, because if one disk fails, data can be rebuilt. Only one disk in the RAID 3 logical drive is reserved to provide redundancy. HP NetRAID Series firmware optimizes RAID 3 data flow for long, serial data transfers such as video or imaging applications. RAID 3 Disadvantages Performance is slower than RAID 0 or RAID 1. RAID 3 Summary Choose RAID 3 if cost, availability, and performance are equally important. RAID 3 performs best when long, serial transfers account for most of the reads and writes. 18