What
is RAID?
A technique was
developed to provide speed, reliability, and increased storage capacity using
multiple disks, rather than single disk solutions. RAID takes multiple hard
drives and allows them to be used as one large hard drive with benefits
depending on the scheme or level of RAID being used. The better the RAID
implementation, the more expensive it is. There is no one best RAID
implementation. Some implementations are better than others depending upon the
actual application. It used to be that RAID was only available in expensive
server systems.
About
Information has
become a commodity in today's world, and protecting that information has become
mission critical. The Internet has helped push this information age forward.
Popular websites process so much information, that any type of slowdown or
downtime can mean the loss of millions of dollars.
RAID
3
This level uses byte
level striping with dedicated parity. In other words, data is striped across
the array at byte level with one dedicated parity drive holding the redundancy
information. The idea behind this level is that striping the data increases
performance and using dedicated parity takes care of redundancy. Three hard
drives are required, two for striping and one as dedicated parity drive.
Although the performance is good, the added parity does slow down writes. The
parity information has to be written to the parity drive whenever a write
occurs.
Raid
5
RAID 5 uses block
level striping and distributed parity. This level tries to remove the bottleneck
of the dedicated parity drive. With the use of a distributed parity algorithm,
this level writes the data and parity data across all the drives. Basically,
the blocks of data are used to create the parity blocks, which are then stored
across the array. This removes the bottleneck of writing to just one parity
drive. However, the parity information still has to be calculated and written
whenever a write occurs, so the slowdown involved with that still applies. The
fault tolerance is maintained by separating the parity information for a block
from the actual data block.
Parity
This is the method by
which a check bit is added to data so that errors can be detected. In a
computer, data is organized into bytes, which consist of a series of eight
bits. These bits are transmitted as a series of on or off signals that
represent the binary values of 1 or 0. A series of O's or 1's can represent an
alphanumeric character or some other type of data. When the simplest form of
parity is used it is usually referred to as Even Parity or Odd Parity. These
two methods add an additional bit to each byte that indicates whether the
number of 1 's in the byte is even or odd.
Conclusion
RAID is a good
solution for companies or individuals craving more transfer performance, redundancy,
and storage capacity in their data storage systems.
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