User`s guide

StorageWorks RAID Array 200 Controller Installation and Standalone Configuration Utility
1–6 EK–SWRA2–IG. C01
1.1.2.4 RAID 5
RAID 5 combines striping (writing data across a set of drives) and redundancy,
as shown in Figure 1–4. RAID 5 provides redundancy by generating parity
information. RAID 5 stripes both segments of data and parity information. If a
single drive fails in a RAID 5 array, you can continue to use the array normally
since the array controller automatically regenerates the data from the failed drive
using data and parity blocks from other operational drives. All data remains
accessible even when one drive fails. However, you can not recover data in the
event of multiple drive failures.
Figure 1–4 RAID 5
Block 0-1
Block 10-11
Parity
Block 2-3
Block 6-7
Parity
Data
Data
Data
Parity
Parity
Parity
SCSI-2
Disk Array Controller
SCSI
SCSI SCSI
Parity
Block 4-5
Block 8-9
In Figure 1–4 each segment is defined as two blocks of 512 bytes each.