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

Vernon,

Comments inline:

> On Behalf Of Vernon Hamberg
> Subject: Re: disk arms (was RE: Tips for user ASP)
>
> If RAID protection is used in the same environment, the DASD arms
become
> the bottleneck. If protection is required, using mirrored arms for the
> journal receiver DASD will provide significantly better performance
than
> RAID protection. However, unprotected DASD arms will allow the highest
> overall transfer rates and best overall performance when using
Opticonnect
> for remote journal.

This makes perfect sense.  In a journal receiver environment, the _only_
regular activity is writes.  Thus there would be no requirement that the
second write be completed if there were only unprotected DASD.

> OTOH, there is a chart showing, in a RAMP-C workload, that mirrored is
> consistently faster than not mirrored.

RAMP-C would include both reads and writes.  I don't know the specific
transactions in the RAPM-C benchmark, but if they mimic standard
business transactions, there should be considerably more reads than
writes.  Thus the benefit of having two disks available for reads must
outweigh the requirement of dual writes when compared to unprotected
DASD.

Regards,
Andy Nolen-Parkhouse