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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 Thecus N199 supports JBOD standard, and RAID 1 with an attached eSATA
hard disk. 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 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 into a single virtual one. As the name implies, disks
are merely concatenated together, end to beginning, so they appear to be a
single large disk.
As the data on JBOD is not protected, one drive failure could result total data loss.