User`s guide

A-6
Storage Concepts
Redundancy
Redundancy refers to the capability of preventing data loss if a disk
drive fails. Some array types give you this capability in one of two
methods:
■ Two identical copies—Data is written to partitions on two disk
drives, resulting in the same data being stored in two places.
Mirror sets, for example, use this method.
■ Parity—Error correction information is distributed across
partitions on three or more disk drives. The error correction
information permits the system to rebuild the data if one drive
fails. RAID 5 sets, for example, use this method.
Array Types
Table A-1 describes the most common types of arrays. Each is
described in more detail in the sections that follow.
Table A-1. Common Array Types
Array Type Strengths Weaknesses
Vol ume Set ■ Low cost ■ No data protection
■ Lower performance
than RAID sets
Stripe set
(RAID 0)
■ Highest performance
■ Supports multiple
simultaneous read and
write operations
■ No data protection; if
one disk drive fails, all
data is lost
Mirror set
(RAID 1)
■ Very high data protection
■ Very high performance for
read-intensive
applications
■ High cost for
redundancy overhead,
because twice the
storage capacity is
required