Intel SRCMR, User Manual

Page: 15 / 180

Introduction and General Information 15
RAID 4 - Data Striping with a Dedicated Parity Drive
RAID 4 works in the same way as RAID 0. The data is striped across the hard disks and the
controller calculates redundancy data (parity information) that is stored on a separate hard disk
(P1, P2). Should one hard disk 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 is needed for redundancy. For example, in a
RAID 4 disk array with 5 hard disks, 80% of the installed hard disk capacity is available as user
capacity, only 20% is used for redundancy. In systems with many small data blocks, the parity hard
disk becomes a throughput bottleneck. With large data blocks, RAID 4 shows significantly
improved performance. RAID 4 requires a minimum of three disks.
Figure 4. RAID 4
RAID 5 - Data Striping with Striped Parity
Unlike RAID 4, the parity data in a RAID 5 disk array are striped across all hard disks. 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 disk 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.