Re: Question about drive configuration

[Philipp Rusch <Philipp.Rusch@xxxxxxxxxxxx>]

No, no !
It's like that:
If you have just 4 drives, all of them are used for the "extra" parity 
information to be stored.
You loose about 20% of total capacit, compared to mirroring (50% loss) this is 
okay.
If you now add another 5th., 6th or 7th drive of equal size to the same 
controller, all of these
disks are secured by the "extra" parity info of the first 4 drives and the 5th, 
6th and 7th keep
their original size. If you give DST a whole bunch of 8 drives at once to make 
up a parity set
a different algorythm is used, that is, the set is made from 8 drives instead 
of 4 and you only
loose about 10% of capacity for parity info, which is now equally spread over 
all 8 disks.
This is the most economic way to add drives on an AS/400 system.
To my mind you would be far better off to get the whole bunch of 10x 4GB drives 
(cheap to get)
for your 170 (thats the max it can hold) and then start an ASP balancing to 
spread the data
over all drives (look at your percentages of disk usage, to "expensive" disks 
aren't used at all).

Regards, Philipp


David Gibbs schrieb:

> "Philipp Rusch" <Philipp.Rusch=pGRmi0hY2G3ucvZx32VAuQ@public.gmane.org>
> wrote in message 3D406B7A.F85BC161@rusch-edv.de">news:3D406B7A.F85BC161@rusch-edv.de...
> > Hello David,
> > you would need another two 8 GB drives to accomplish your task,
> > the AS/400 RAID algorythm needs 4 drives of equal type for a parity set.
> > So what your SE did was the best thing he could do a that time.
> > > # Type   Size  % used  Protection
> > > 1 6607   4194  91.9 1  DPY
> > > 2 6607   3145  92.4 1  DPY
>
> What about unit #1?  That's not the same size as the others... or is that
> because it's the load source?
>
> david