Specifications

SCSI to SATA RAID Subsystem | Administrator’s Manual RAID Functions: Introduction | en 9
Bosch Security Systems F.01U.027.802 | V1 | 2006.11
1 RAID Functions: Introduction
Redundant Arrays of Independent Disks, or RAID, offers the following advantages: availability,
capacity, and performance. Choosing the right RAID level and drive failure management can
increase capacity and performance, subsequently increasing availability. Bosch's external
RAID controllers and subsystems provide complete RAID functionality and enhanced drive fail-
ure management.
1.1 Logical Drive
The advantages mentioned above are achieved by creating “logical drives.” A logical drive is an
array of independent physical drives. The logical drive appears to the host as a contiguous vol-
ume, the same as a local hard disk drive does.
Fig. 1.1 Logical Drive
The following section describes the different methods to create logical arrays of disk drives,
such as spanning, mirroring and data parity. These methods are referred to as “RAID levels.”
1.2 Logical Volume
The concept of a logical volume is very similar to that of a logical drive. A logical volume is the
combination of one or several logical drives. These logical drives are combined into a larger
capacity using the RAID0 method (striping). When data is written to a logical volume, it is first
broken into data segments and then striped across different logical drives in a logical volume.
Each logical drive then distributes data segments to its member drives according to the spe-
cific RAID level it is composed of.
The member logical drives can be composed of the same RAID level or each of a different RAID
level. A logical volume can be divided into a maximum of 8 partitions. During operation, a host
computer sees a non-partitioned logical volume or a partition of a logical volume as one single
physical drive.