Re: New RAID-5 algorithm on V4R5 ?

[Larry Bolhuis <lbolhuis@xxxxxxxxxx>]

Philipp,

  It's the new math!

  Actually you have fallen into the trap of picking a percentage which
is not correct.  To calculate storage lost to RAID you simply subtract
the capacity of 1 disk from the set. This will range from a high of 25%
on the smallest set (1 disk of 4) to a low of 10% on the largest sets (1
disk of 10).

  Note that the amount lost per drive varies as the RAID data is kept on
either 4 or 8 drives depending on the total number of drives in the set.
(4 drives for sets of 4 to 7 drives and 8 drives for sets of 8 to 10
drives).  Thus WRKDSKSTS will report different sizes for the drives
carrying RAID data than those that are not.

  Likely your 170 has 10 drives (1 of 10 lost to RAID) and your 620 had
5 (1 of 5 lost).

 HTH - Larry

Philipp Rusch wrote:
> 
> Hi all,
> 
> I noticed while being at a transition job from one AS/400 to another,
> that there is a difference in how V4R4 and V4R5 handles disk sets on
> a 2740 controller.
> I used to calculate the resulting capacity when "raiding" a set of disks
> on a 274x controller as a loss of about 20% of total capacity.
> When working on a 620-2179 with V4R4 and 6713 disks (8.58 GB)we
> got a resulting capacity of about 6400 MB each, the same disks gave
> me round about 7512 MB on a system 170-2385 with V4R5 and both systems
> were using a 2740 RAID controller.
> Looks to me as if we have a better algorithm as before, because only
> about 10% is used up for running RAID-5 on that set.
-- 
Larry Bolhuis
Arbor Solutions, Inc.
(616) 451-2500
(616) 451-2571 -fax
lbolhuis@arbsol.com
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