Intel SRCU31, User Manual

Page: 15 / 182

Introduction and General Information 15
RAID 4 - Data Striping with a Dedicated Parity Drive
RAID 4 (Figure 3) works in the same way as RAID 0. The data is striped across the hard disk
drives and the controller calculates redundancy data (parity information) that is stored on a separate
hard disk drive (P1, P2). Should one hard disk drive fail, all data remains fully available. Missing
data is recalculated from existing data and parity information.
Unlike in RAID 1 only the capacity of one hard disk drive is needed for redundancy. For example,
in a RAID 4 disk array with five hard disk drives, 80% of the installed hard disk drive capacity is
available as user capacity, only 20% is used for redundancy. In systems with many small data
blocks, the parity hard disk drive becomes a throughput bottleneck. With large data blocks,
RAID 4 shows significantly improved performance. RAID 4 requires a minimum of three disks.
Figure 3. RAID 4