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Number   :  1603
Date     :  2002-02-15
Author   :  rotaiv
Subject  :  Re: Hello?... File Size Limitations?
Size(KB) :  1


Bob,

Depending on who you ask, you are likely to get different definitions of 
RAID 0 through RAID 4. However, I think you will find that most people 
agree RAID 5 is 3 or more disks combined together with the data "stripped" 
over all three disks. Two disks are used for data and the third disk is 
used for the block check-sum. The idea is that if any one of the disks 
fail, the other two can be used to retrieve the information with no data 
loss. Performance will be degraded because each block has to have the 
missing information reconstructed from the data that is still 
available. If you lose two or more disks in a RAID 5 array, you will lose 
all the data.

Most implementations of RAID 5 have a "hot spare" or extra hard drive that 
is waiting to be used. When one of the drives in the RAID fails, this 
drive comes on-line, the data is reconstructed and the RAID becomes 100% 
again. The dead drive is then replaced and a new hot spare inserted ready 
for the next drive failure. I have personally built many hardware RAID 5 
implementations and can attest that RAID works and it has saved the day 
numerous times.

rotaiv.



At 02/15/2002 11:00 AM, Bob Weir wrote:

>I understood RAID 0 shared data between disks to give faster access but it
>then becomes susceptible to failure of either disk (a reduced MTBF) whereas
>RAID 1 duplicates data on each disk giving slower access but enhanced
>security (either disk can fail without loss). There is a version of RAID
>which both shares and duplicates using four disks but I have never
>investigated (or justified) that, since my current machine only has two
>connectors left which are available for HD's.
>
>regards,
>
>Bob Weir
>
>
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