HP SureStore E Disk Array FC60 Service Manual (A5635A)

48 Disk Array High Availability Features
using a 5-disk RAID 5 volume group, a stripe segment size of 32 blocks (16
K
B) would
ensure that an entire I/O would fit on a single stripe (16
K
B 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.