RE: disk arms (was RE: Tips for user ASP)

R. Bruce,

Our production as400s run fully mirrored, with each pair in a different rack
and controller.  I understand that this improves our ability to continue
operations in the event of loss of power to a single rack.  I wondered once
if a mirrored configuration outperforms RAID by allowing read operations to
go to either disk (first unit is busy with another read, second unit takes
over an fetches the data).  I guess that would be: "Are the arms of a
mirrored pair independent of each other (for asynchronous reads)?"

Also, isn't mirroring considered a form of RAID?  I seem to recall RAID
having a number associated to indicate the form of RAID being implemented.
RAID 5 is the data-striping method, RAID 1 is mirroring..... (?)

Eric DeLong
Sally Beauty Company
MIS-Project Manager (BSG)
940-898-7863 or ext. 1863



> -----Original Message-----
> From: R. Bruce Hoffman, Jr. [mailto:rbruceh@attglobal.net]
> Sent: Friday, June 28, 2002 11:58 AM
> To: midrange-l@midrange.com
> Subject: Re: disk arms (was RE: Tips for user ASP)
>
<SNIP>The one
> that is not (believe it or not) is fully mirrored. As for the
> arms, you hit
> the problem squarely. No one, not even programmers, is able
> to look at a
> disk that is 20% full and think they need more arms.
>
>
> ===========================================================
> R. Bruce Hoffman, Jr.
>  -- IBM Certified Specialist - iSeries Administrator
>  -- IBM Certified Specialist - RPG IV Developer
>
> "There is a crack in everything,
>   that's how the light gets in.
>     - Leonard Cohen
>