RAID is Not a Backup Solution
Author: Michael J. Leaver, 2BrightSparks
PDF version [opens
There are some who believe a RAID array
provides a backup solution. It does not.
This article informs users about some
of the common misconceptions about RAID,
how backing up using software is crucial
in preventing data loss.
A Definition of
For those unfamiliar with the term RAID, here
is how Wikipedia defines it:
|In computing, the acronym RAID
(Redundant Array of Inexpensive (or
Independent) Drives (or Disks)) is
an umbrella term for data storage
schemes that divide and/or replicate
data among multiple hard drives.
Its benefits, varying by scheme,
are increased data reliability and/or
…Fundamentally, RAID combines
multiple hard disks into a single
logical unit. There are two ways
this can be done: in hardware and
in software. Hardware combines
the drives into a logical unit
in dedicated hardware which then
presents the drives as a single
drive to the operating system.
Software does this within the operating
system and presents the drives
as a single drive to the users
of the system... RAID is typically
used on servers but can be used
simpler terms: RAID enables the use of multiple
drives (an array of drives) to increase drive
performance and/or reliability. There are many
types (levels) of RAID which can be implemented
using software or hardware. Many modern motherboards
include hardware RAID support.
RAID 0 (Striped Set)
With two or more drives, and a motherboard
that supports it, you can theoretically increase
your drives performance by using RAID 0 (also
called a Striped Set). This is the method where
a file’s data is scattered across all
the drives. Although a striped set can increase
performance, it also increases the chances
of data loss (the more drives in the array,
the higher the risk). This is because if just
one of the drives fails, then all files will
With RAID 0 the chances of data loss is increased.
In this scenario using a backup solution is
Other RAID levels, e.g. Mirrored Set
The other RAID levels, e.g. RAID 1 (Mirrored
Set), decrease the chance of data
loss. This is done by essentially duplicating data across the drives in the array.
If a file becomes corrupted (or even lost) due to drive failure, then a copy
of the file can be retrieved from another drive. This is all done automatically
without user intervention.
The important point to note however is that although the chance of data loss
due to drive failure is reduced, data loss due to viruses or user errors, e.g.
overwriting a file or deleting it, is not. If a file is deleted or overwritten
the RAID array cannot be used to retrieve it. The file is gone. When a file
is deleted it is deleted from all the drives. When a file is overwritten it
is overwritten on all the drives. This is why a RAID array is not a backup
Backup is still required with RAID
There is no doubt that RAID speeds up
data access and/or makes access more reliable,
but do not be lulled into a false sense of
security. RAID may reduce the chance of losing
data due to drive failure but it is no protection
against losing your data due to other means,
e.g. user error.
your important files today and don’t
be fooled into thinking RAID is a backup solution.
For more information and guidance about backing
up read The