What is RAID? |
RAID(redundant array of
inexpensive disks) is a system which uses multiple hard drives
to share or replicate data among the drives so that data is
backed up in real time or arranged so that the read/write
speed is dramatically enhanced.
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Why RAID? |
 Increased
data protection. If in an unfortunate event where a drive
fails, the same data is preserved on the mirrored drive. |
Intelligent
array controllers can apply different types of RAID for
different hard disk drives. |
Increased overall network system data capacity.
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Increased
I/O read/write efficiency. |
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Detailed descriptions are provided below to depict how those RAID systems operate. |
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RAID 0 -
Striping |
RAID 0 is data that is
split in between two hard drives. The data is also
accessed the same way making data read and write
faster.The recovering of data is impossible if any one
of the disks is damanged.
RAID 0 requires at
least two hard drives, e.x.: 400GB + 120GB =
520GB |
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Read and write access times are
increased. |
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Data is not redundant so 100% of the two
or more disks can be used. |
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There is no redundancy so no data is
recoverable if one drive is damaged. |
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There is no security with RAID 0, only
performance. |
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High speed Read/Write applications where
backup and security is not important. |
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RAID 1 -
Mirroring |
RAID 1, data is
mirrored so the exact same data is stored on two
different hard drives. The data is identical and used
for backup purposes. If one hard drive fails, the second
one can be used to create another copy.
RAID 1
requires a minimum of 2 hard drives, e.x.: 400GB
+ 120GB = 120GB |
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Simple RAID application. |
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100% backup of hard drive in case one
drive fails. |
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RAID 1 uses more system resources. |
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RAID 1 uses one hard drive for backup,
the cost of two drives will only store the size of the
samllest hard drive size. |
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When two drives have different spec, the
inferior one will have negative effect on the
transferring speed of the RAID 1 as a
whole. |
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Systems that require backup of important
files. |
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RAID 5 -
Striping with Rotating Parity |
RAID 5 makes a copy of
a file and splits that copy among the different hard
drives in the array while keeping a copy of the file in
one of the many drives. If one drive fails, then the
copies on the other drives can replace and re-create the
files from the damaged drive.
RAID 5 requires at
least 3 drives, e.x.: 400GB + 300GB + 120GB =
240GB |
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The time needed for data transferring is
only next to the RAID 0. |
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Able to use more hard drive space
compared to RAID 1. |
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Takes longer to rebuild a damaged drive
compared to RAID 1. |
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General File Server. |
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Database Server. |
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Web and mail servers. |
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RAID 0+1 (RAID
10) - Mirror + Striping |
RAID 0 + 1(RAID 10).
They are two stage RAID configurations. In RAID 0 + 1,
the base level is striping and on the second level is
mirroring. Essentially RAID 0 + 1 is mirroring RAID 0
arrays while RAID 0 is striping two RAID 1
arrays.
RAID 0 + 1 (RAID 10) requires 4 hard
drives or more, e.x.: 400GB + 400GB + 400GB +
400GB = 800GB |
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Performance of RAID 0 and security of
RAID 1. |
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Costly. 4 drives only store the same
smount as 2 drives. |
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General File Server. |
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Large capacity image files. |
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JBOD or Linear |
Individual disk. This mode doesn't provide
redundancy.
Only need one hard drive, e.x.: 400GB / 300GB = 400GB / 300GB
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No redundancy for backup. |
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There is no additional efficiency or
backup functions. |
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BIG |
Several physical disks combined as a logical disk. In
other words, the capacity of the logical drive is the
total capacity of the physical drives. This mode doesn't
provide redundancy.
BIG requires two or more
drives, e.x.: 400GB + 120GB = 520GB
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Will hold more space than a virtual
drive. |
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Large files will flow over to the next
drive. |
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Effective use of hard drive space. |
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There is no additional efficiency or
backup functions. |
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