Understanding Raid; Raid 0; Raid 1 - Xerox SAFEStor User Manual

SAFEStor User Guide
U nd ersta n din g R A ID
RAID is an acronym for Redundant Array of Independent Disks. A RAID system consists of an
array of multiple independent hard disk drives that provide high performance and fault tolerance.
The RAID controller implements several levels of the Berkeley RAID technology. An
appropriate RAID level is selected when the volume sets are defined or created. This decision is
based on disk capacity, data availability (fault tolerance or redundancy) and disk performance.
The RAID controller makes the RAID implementation and the disks physical configuration
transparent to the host operating system. This means that the host operating system drivers and
software utilities are not affected, regardless of the RAID level selected. Correct installation of
the disk array and the controller requires a proper understanding
of RAID technology and the concepts.

RAID 0

RAID 0, also referred to as striping, writes stripes of data across multiple disk drives. RAID 0
does not provide any data redundancy, but does offer the best high-speed data throughput. RAID
0 breaks up data into smaller blocks and then writes a block to each drive in the array. Disk
striping enhances performance because multiple drives are accessed simultaneously; but the
reliability of RAID Level 0 is less than any of its member disk drives due to its lack of
redundancy.

RAID 1

RAID 1 also known as "disk mirroring", means that data written to one disk drive is
simultaneously written to a second disk drive. Read performance may be enhanced if the array
controller can simultaneously access both members of a mirrored pair. During writes, there will
however, be a minor performance penalty when compared to writing to a single disk as two
writes must occur (one to each disk drive). If one drive fails, all data (and software applications)
is preserved on the other drive. RAID 1 offers extremely high data reliability, but at the cost of
doubling the required data storage capacity.
Page 2