Re: RAID -v- Mirroring (was New RAID-5 algorithm on V4R5 ?)

Phillip,

  Glad I won you over!!  And you (and Neil) are correct about adding
disks - When you are going to exceed 7 in the set you need to stop and
re-start.

  As for RAID -v- Mirroring, We sell virtually 100% RAID.  It's cheaper
and the protection is adequate for most users needs.  However, Mirroring
does provide better protection and it can be substantially better if
enough equipment is purchased.  It also will perform better in a Read
Intensive environment and some will argue (here's where we'll probably
hear from the Geezer in Gig Harbor) that even in a write intensive
invironment it is better.

  Certainly performance during a failure is better although we have not
seen the dramatically reduced performance of RAID with a failed unit.
Also I am not aware of any additional restrictions when replacing a
failed unit in a Mirrored setup as compared to RAID.

  - Larry

Philipp Rusch wrote:
> 
> Larry,
> 
> okay, okay, you are right.
> I thought that, when you start with a RAID set, of lets say 4 drives à 8.58 
>gb,
> then you add up to three, which are still "under protection" of the first 4 
>forming
> the RAID set, then you have full capacity with those three additional disks.
> No you carry on adding disks and get another set of four (reducing capacity ?)
> until you add more disks than 8, 12, 16 ....
> (What I was guessing when looking at AS/400 RAID was a modulo 4 scheme)
> But I missed the fact, that there is a change in handling, when you add all 
>disks
> at once. So there must be two different "algorithms".
> As Neil Palmer stated somewhere else on this list, you should stop parity
> protection when adding more than 3 disks of equal size to a RAID set, after 
>adding
> to your config, you start it again and get RAID info spreaded in a new 
>fashion.
> 
> OK.
> Lets perhaps discuss a new theme:
> 
> What do you prefer: RAID-5 or good old mirroring ?
> 
> I had several disk failures at my customers machines and RAID-5 was awfully 
>slow
> when one disk was failing ... about 10 - 20% of normal performance.
> Okay we did not loose any data, but mirroring is still the better way to keep 
>on with
> your business like nothing happened .. except you need to call a technician 
>to replace
> a disk.
> 

-- 
Larry Bolhuis
Arbor Solutions, Inc.
(616) 451-2500
(616) 451-2571 -fax
lbolhuis@arbsol.com
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