Raid Types; Raid 5 Group (Individual Access Array) - EMC CX700 Planning Manual

RAID Types and Trade-offs

RAID Types

RAID 5 Group (Individual Access Array)

2-4 EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide
You can choose from the following RAID types: RAID 5, RAID 3,
RAID 1, RAID 0, RAID 1/0, individual disk unit, and hot spare.
You can choose an additional type of redundant disk — a remote
mirror — for any RAID type except a hot spare.
A RAID 5 Group usually consists of five disks (but can have three to
sixteen). A RAID 5 Group uses disk striping. With a RAID 5 group,
you can create up to 128 RAID 5 LUNs to apportion disk space to
different users, servers, and applications.
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.
Figure 2-2 shows user and parity data with the default stripe element
size of 128 sectors (65,536 bytes) in a five-disk RAID 5 group. The
stripe size comprises all stripe elements. Notice that 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.