HP Surestore Disk Array FC60 HP SureStore E Disk Array FC60 Service Manual (A5 - Page 48
RAID Levels, RAID 0
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using a 5-disk RAID 5 volume group, a stripe segment size of 32 blocks (16 KB) would ensure that an entire I/O would fit on a single stripe (16 KB on each of the four data disks). The total stripe size is the number of disks in a volume group multiplied by the stripe segment size. For example, if the stripe segment size is 32 blocks and the volume group comprises five disks, the stripe size is 32 X 5, or 160 blocks (81,920 bytes). RAID Levels RAID technology uses a number of different techniques for storing data and maintaining data redundancy. These industry-standard RAID levels define the method used for distributing data on the disks in a volume group. Volume groups that use different RAID levels can be created on the same disk array. The Disk Array FC60 supports the following RAID levels: • RAID 0 • RAID 1 • RAID 0/1 • RAID 3 • RAID 5 RAID 0 RAID 0 uses disk striping to achieve high performance. Data is striped across all disk in the volume group. The ability to access all disks in the volume group simultaneously provides a high I/O rate. Unlike the other RAID levels, RAID 0 does not provide any data redundancy, error recovery, or other high availability features. Consequently it should not be used in environments where high-availability is critical. which is why it is not supported. RAID-0 provides enhanced performance through simultaneous I/Os to multiple disk modules. A RAID 0 group configuration for a logical disk unit offers fast access instead of high availability. Software mirroring the RAID-0 group provides high availability. Figure 18 illustrates the distribution of user and parity data in a four-disk RAID 0 volume group. The the stripe segment size is 8 blocks, and the stripe size is 32 blocks (8 blocks times 4 disks). The disk block addresses in the stripe proceed sequentially from the first disk to the second, third, and fourth, then back to the first, and so on. 48 Disk Array High Availability Features