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

Bruce, check your computer date. It says I received this e-mail
5/30/2002.

-----Original Message-----
From: midrange-l-admin@midrange.com
[mailto:midrange-l-admin@midrange.com] On Behalf Of R. Bruce Hoffman,
Jr.
Sent: Friday, June 28, 2002 3:41 PM
To: midrange-l@midrange.com
Subject: Re: disk arms (was RE: Tips for user ASP)

----- Original Message -----
From: "DeLong, Eric" <EDeLong@Sallybeauty.com>
To: <midrange-l@midrange.com>
Sent: Friday, June 28, 2002 3:27 PM
Subject: RE: disk arms (was RE: Tips for user ASP)


> 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)?"

Reads are about the same... the real performance boost on mirroring
comes
from writes.

> 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..... (?)

Yup. mirroring is described in the original raid docs, but I consider
them
as two different beasts. Raid usually requires special hardware (raid
controllers, iops) whereas mirroring is done by the system and can be
done
at device, iop or bus level. Raid is a set on a controller.

===========================================================
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



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