RE: Performance 810 vs. 820 -- MIDRANGE-L

Oliver,

Replies inline.

Regards,
Andy Nolen-Parkhouse

> On Behalf Of ouuch@xxxxxxxxxxx
> Subject: Performance 810 vs. 820
> 
> Hi,
> 
> we have an 820 (FC2396 - 950/250 CPW) and an 810 (about 1100 CPW) as
> backup system.
> DASD performance is nearly maxxed out (mirrored 6718 drives for 193GB)
> on the 820.
> 
> Any ideas how the 810 with 10 RAIDED 35GB drives will perform (280GB
> netto)? With our
> current data, the 810 is at 50% DASD, the 820 is around 75%, partially
> going above 80%.

Your capacity and your disk performance are often entirely separate.  How
many disk arms do you have on the 820?  I calculate 22 (11 pairs) from
your capacity above.  If this is true you have 11 arms available for
writes and 22 arms available for reads.  Depending on your 35 GB drives,
you may have a faster rotational speed than your 17.5 GB drives.  The
#4326 drive has a 15 K RPM and the #4319 has a 10 K RPM.  The faster
drives would give you better performance for some types of disk
operations, although not significantly so for the random access typically
required for interactive performance.

You also need to consider the specific RAID controller you are using.
How fast is it and how much write cache does it have?

It's probably too complex to get a definitive answer, even if you had
given all of technical details.  My gut reaction is that the 810 (10 35
GB drives RAIDed) will not be different enough from the 820 (22 17.5 GB
drives mirrored) to make a difference.  If DASD performance is maxed out
on the 820, your 810 configuration may not take to far enough back from
the knee of the performance curve, and may actually provide less
performance.  The unknown in making that judgment is the specific
controller on the 810.  IBM has made some impressive claims for the #2757
PCI-X Ultra RAID Controllers.  It could make a difference.

> In December, we will be looking for a replacement for the 820. Am I
> right there are no upgrade
> paths for the 810 (even the biggest)? The next bigger model would be
> the 825, yes?

I believe your understanding on upgrades is correct.  Your existing 820
could be upgraded to a quad-processor with 3700 CPW and your existing 810
could be upgraded to a two-way at 2700 CPW.  Both have plenty of room for
adding additional disk drives.  If you're looking for a short-term
solution, your most economical path might be to upgrade the 810 and use
it for production, then swap the 820 to backup status.

If you want to replace the 820 with new hardware and preserve a
relatively infinite upgrade path, then the 825 would be your choice.  You
would jump to 3600 CPW (minimum with 3 processors) and might well go into
sticker shock at the price of an enterprise package.