HP LH4r Installation and configuration of the HP NetRAID, NetRAID-1 and NetRAI - Page 27

Chapter 2 RAID Overview RAID 5: Striping with Distributed Parity RAID 5 is the most common configuration because it provides good overall performance and data protection with a minimum loss of storage capacity. RAID 5 distributes the parity blocks equally among all disk drives to achieve better overall performance than if a dedicated parity disk is used (RAID 3). If you have five physical drives configured as one RAID 5 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 Parity 9-12 Block 4 Parity 5-8 Block 11 Parity 1-4 Block 8 Block 12 RAID 5 outperforms RAID 1 for read operations. The write performance, however, may be slower than RAID 1, especially if most writes are small and random. For example, to change Block 1 in the diagram above, the HP NetRAID Series adapter must first read Blocks 2, 3, and 4 before it can calculate Parity Block 1-4. Once it has calculated the new Parity Block 1-4, it must write Block 1 and Parity Block 1-4. RAID 5 Advantages There is no data loss or system interruption due to disk failure, because if one disk fails, data can be rebuilt. Capacity equivalent to only one disk in the RAID 5 logical drive is reserved to store redundant data. RAID 5 outperforms RAID 1 for read operations. RAID 5 gives good performance if you have a high volume of small, random transfers. RAID 5 Disadvantages Write performance is slower than RAID 0 or RAID 1. RAID 5 Summary Choose RAID 5 if cost, availability, and performance are equally important. RAID 5 performs best if you have I/O-intensive, high read/write ratio applications such as transaction processing. 19