Re: Question about drive configuration

[Philipp Rusch <Philipp.Rusch@xxxxxxxxxxxx>]

Let me refine my calculation about disk config with 4 GB drives
Option 1 - you cannot exchange the 8 GB drives and have to buy another 2x 8GB 
to form
a RAID set - you have 5x 4GB and 4x 8GB then, which gives you roughly 4x 3 GB + 
4 GB
and 4x 6.5 GB = 16 GB + 26 GB = 42 GB as total size and one disk slot left over.
Option 2 - you exchange (somehow ;-) ) the 8 GB drives and fill up any slots 
with old and cheap
4 GB drives this gives you 8x 4 GB minus 10% = 29 GB + 8 GB = 37 GB and adds 
the possibility
to  spread data over 10 equal disk arms.

just my two cents from over the big lake ... Philipp

Philipp Rusch schrieb:

> 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
>