Re: New RAID-5 algorithm on V4R5 ? -- MIDRANGE-L

Hello Larry,

Obviously, youre right !

But you are only near the complete truth ...

The 620 we were moving from had 5 disks 4.1 gb and 5 disks 8.5 gb,
like this, 4 disks of each size form a RAID set and the fifth disk of each
set is protected by the others of same size  -  agreed.
But, the new 170 is equipped with 10x 8.5 gb and is also having 2 disks
with complete capacity and 8 disks with reduced capacity, which I would
expect to have the same size as with the 620 because every 4 disks form
a set ... (?)

Still no clue what is this new math now,

regards, Philipp

Larry Bolhuis schrieb:

> 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

+---
| This is the Midrange System Mailing List!
| To submit a new message, send your mail to MIDRANGE-L@midrange.com.
| To subscribe to this list send email to MIDRANGE-L-SUB@midrange.com.
| To unsubscribe from this list send email to MIDRANGE-L-UNSUB@midrange.com.
| Questions should be directed to the list owner/operator: david@midrange.com
+---