RE: iSeries Disk Pricing

["Andy Nolen-Parkhouse" <aparkhouse@xxxxxxxxx>]

Paul,

I agree with your point, but I'm not sure that the #4318 (17 GB 10K
drive) and the #4317 (8.5 GB 10K) differ significantly in cache or data
transfer characteristics.  The V5R1 Performance Capabilities Reference
describes them as being similar but for capacity (it doesn't get
specific on the characteristics you reference).  They are both Ultra2
SCSI at 80 MB transfer rates.  I think that they are pretty much apples
and apples in their performance characteristics.  So pending any
announcements of new disk drives, I would stand by my main points.  I
agree that room for expansion is a good thing, but in the case of many
of the systems I configured, they already had room for many years of
expansion using the 8 GB drives.

Increasing system memory would provide significant throughput
improvements for both 8 GB and 17 GB configurations.

Syd,

I agree with your point that other workloads, including those dealing
with stream files, may not be affected as dramatically, my comments were
referring specifically to DB2-based transaction serving, whether
green-screen or client-server.

Regards,
Andy Nolen-Parkhouse

> Subject: Re: iSeries Disk Pricing
>
> While the number of arms is of course, very important, the cache in
the
> DASD and the
> speed with which the DASD can transfer data has a perhaps,
unexpectedly
> large impact
> on overall performance.
>
> You *might* find that you only need 1/2 the number of arms to get the
same
> or better
> performance. It depends a lot on your system and application, but that
is
> definitely a
> possibility. As well as the fact that databases tend to grow and grow,
and
> DB/2, unlike
> traditional file based systems, can also partition the data in better
> ways, allowing you to
> partition data for a particular system (or geographic location, or
group
> of users, etc.) over
> a particular set of volumes.
>
> -Paul