77
Appendix C: RAID Basics
Overview
A Redundant Array of Independent Disks (RAID) is an array of several hard disks that
provide data security and high performance. A RAID system accesses several hard disks
simultaneously, which improves I/O performance over a single hard disk. Data security is
enhanced by a RAID, since data loss due to a hard disk failure is minimized by regenerating
redundant data from the other RAID hard disks.
Benefits
RAID improves I/O performance, and increases data security through fault tolerance and
redundant data storage.
Improved Performance
RAID provides access to several hard disk drives simultaneously, which greatly increases I/O
performance.
Data Security
Hard disk drive failure unfortunately is a common occurrence. A RAID helps prevent against
the loss of data due to hard disk failure. A RAID offers additional hard disk drives that can
avert data loss from a hard disk drive failure. If a hard drive fails, the RAID volume can
regenerate data from the data and parity stored on its other hard disk drives.
RAID Levels
The ALLNET ALL6501 supports standard RAID levels 0, 1 and JBOD. You choose a RAID level
when you create a system volume. The factors for selecting a RAID level are:
•
Your requirements for performance
•
Your need for data security
•
Number of hard disk drives in the system, capacity of hard disk drives in the system
The following is a description of each RAID level:
RAID 0
RAID 0 is best suited for applications that need high bandwidth but do not require a high
level of data security. The RAID 0 level provides the best performance of all the RAID levels,
but it does not provide data redundancy.
RAID 0 uses disk striping and breaking up data into blocks to write across all hard drives in
the volume. The system can then use multiple hard drives for faster read and write. The
stripe size parameter that was set when the RAID was created determines the size of each
block. No parity calculations complicate the write operation.
RAID 1
RAID 1 mirrors all data from one hard disk drive to a second one hard disk drive, thus
providing complete data redundancy. However, the cost of data storage capacity is doubled.
This is excellent for complete data security.
JBOD
Although a concatenation of disks (also called JBOD, or "Just a Bunch of Disks") is not one of
the numbered RAID levels, it is a popular method for combining multiple physical disk drives
