Re: What is RAID!

[Mark Komarinski <markk@cgipc.com>]

There are a few RAID levels that describe different things.  Some RAID levels
are for performance, some are for high availability.

RAID 0 covers writing the same data to two identical disks.  If one fails,
the other one picks right up.
RAID 1 covers writing alternate bytes to two identical disks.  If one fails,
you lose all your data, but since writing data to the drive is a relatively
slow process, you (theoretically) double the access to your drives.
RAID 2, 3, 4 aren't used much, but cover things like separate parity disks to
rebuild a failed drive.  If one drive fails, you're okay, but if the
parity disk fails, it's gone.
RAID 5 is probably the most popular, since it gives a great balance of
HA and performance.  For N disks in your system, you get N-1*(size of drive)
space available.  In my RAID 5 configuration, I have three 4.5 GB drives,
which gives me a total space of 9.0GB.  The missing 4.5GB is filled with
parity and ECC data to allow the entire system to run if one drive fails.
If two fail, you're sunk.  Since data is scattered among all the drives,
you get a great thruput of read and write.

-Mark

luser@texas.net wrote:
> 
> Hello!
> 
>   A RAID is just a bunch of Hard Disks that are writen to at the same time so
> that you have a backup.  Imagine a server with 5 Hard Disks, well you
> read/write to them all.  Well say the main HD goes out you have 4 backup that
> you can fall onto so you dont lose all your important data.
>   If I explaind this wrong please email me, or if anyone can explain it with a
> better analogy PLEASE tell me =)
> 
> mcc

-- 
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Carlo Gavazzi IPC     | Mark F. Komarinski, RHCE - Compat. Engineer|
176 Second Ave        | markk@cgipc.com - www.cgipc.com            |
Waltham, MA 02451 USA | Ph: 781-290-4800 x138  Fx: 781-290-4810    |


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