Randy Harris wrote:
> "Frank van Bortel" <fvanbortel_at_netscape.net> wrote in message
> news:cprmib$q43$1_at_news1.zwoll1.ov.home.nl...
>
>>Jonathan Lewis wrote:
>>
>>>Sorry about the delay in replying. Two weeks
>>>out of the country, and lots to catch up on.
>>>
>>>I rarely get the numbers right, but a fixed parity
>>>disk is either RAID-3 or RAID-4. When you
>>>move to RAID-5, I believe the parity is described
>>>as 'block-level rotating parity', so every disc gets
>>>a fair share.
>>>
>>>A pattern across five disc would look something
>>>like the following (where D = data and P = parity
>>>block).
>>>
>>>D D D D P
>>>D D D P D
>>>D D P D D
>>>D P D D D
>>>P D D D D
>>>
>>
>>RAID-3 as well as 4 have a fixed parity disk.
>>You are correct about RAID-5.
>>
>>In addition to the redundancy in data, the Hamming codes
>>used for parity calculations, can recreate the missing
>>parity bit from remaining disks, thus allowing one disk
>>to go bad.
>>However, 2 bits cannot be recalculated
>>(aka when 2 disks go bad: failure).
>>
>
>
> I've never seen it, but read that someone offers a RAID 6. It doubles the
> parity data, so that recovery can be done in the event of two drives in an
> array failing at the same time.
>
>
>
Yup, see http://www.acnc.com/04_01_06.html. They
also have RAID-50...
--
Regards,
Frank van Bortel
Received on Fri Dec 17 2004 - 13:36:32 CST
