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RAID 4 - Data Striping with a Dedicated Parity Drive
RAID 4 (Figure 4) works in the same way as RAID 0. The data is striped across the hard drives
and the controller calculates redundancy data (parity information) that is stored on a separate hard
drive (P1, P2). Should one hard 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 drive is needed for redundancy. For example, in a
RAID 4 disk array with five hard drives, 80% of the installed hard drive capacity is available as
user capacity, only 20% is used for redundancy. In systems with many small data blocks, the parity
hard drive becomes a throughput bottleneck. With large data blocks, RAID 4 shows significantly
improved performance. RAID 4 requires a minimum of three disks.
RAID 5 - Data Striping with Striped Parity
Unlike RAID 4, the parity data in a RAID 5 disk array are striped across all hard drives (Figure 5).
The RAID 5 disk array delivers a balanced throughput. Even with small data blocks, which are
very likely in a multi-tasking and multi-user environment, the response time is very good. RAID 5
offers the same level of security as RAID 4. When one hard drive fails, all data is still fully
available. Missing data is recalculated from the existing data and parity information. RAID 4 and
RAID 5 are particularly suitable for systems with medium to large capacity requirements, due to
their efficient ratio of installed and available capacity. RAID 5 requires a minimum of three disks.
Introduction and General Information
Figure 4. RAID 4
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