User`s manual

Appendices
Appendix C. RAID Levels
This appendix provides a functional description of Redundant Array of
Independent Disks (RAID). This includes information about RAID and
available RAID levels.
C.1. RAID Description
Redundant Array of Independent Disks (RAID) is a storage technology used
to improve the processing capability of storage systems. This technology is
designed to provide reliability in disk array systems and to take advantage of
the performance gains multiple disks can offer.
RAID comes with a redundancy feature that ensures fault-tolerant,
uninterrupted disk storage operations. In the event of a disk failure, disk
access will still continue normally with the failure transparent to the host
system.
RAID has several different levels and can be configured into multi-levels,
such as RAID 10, 30, and 50. RAID levels 1, 3 and 5 are the most
commonly used levels, while RAID levels 2 and 4 are rarely implemented.
The following sections described in detail each of the commonly used RAID
levels.
RAID offers the advantages of Availability, Capacity, and Performance.
Choosing the right RAID level and drive failure management can increase
data Availability, subsequently increasing system Performance and storage
Capacity. Infortrend external RAID controllers provide complete RAID
functionality and enhance drive failure management.
C.2. Non-RAID Storage
One common option for expanding disk storage capacity is simply to install
multiple disk drives into the system and then combine them end-to-end.
This method is called disk spanning.
In disk spanning, the total disk capacity is equivalent to the sum of the
capacities of all SCSI drives in the combination. This combination appears
to the system as a single logical drive. For example, combining four 1GB
drives in this way would create a single logical drive with a total disk
capacity of 4GB.
Disk spanning is considered non-RAID due to the fact that it provides
neither redundancy nor improved performance. Disk spanning is
inexpensive, flexible, and easy to implement; however, it does not improve
the performance of the drives and any single disk failure will result in total
data loss.
RAID Levels App-13