5820 performance ( IO )

[George Robbins]

In article <1990Oct29.151224.21573 at mlb.semi.harris.com> jdr at jrx.mlb.semi.harris.com (Jim Ray) writes:
> Has anyone had experience with 5820's connected to HSC70's ( with
> RA92's )?
> 
> I have been less than impressed so far with the IO performance and would
> like to find out if anyone else has had similar experiences with the 5820.

I did some simple tests back when we first got our 5810, and concluded the
bottleneck wasn't really the 5810, but rather the HSC50/SDI combination.
The SDI peak bandwidth has fallen below that required to effectively support
state of the art 24M-Bit/Sec drives.  There also seems to be a problem with
the buffering (at least in the HSC50), since the HSC statistics seem to show
a 10-20% NAK rate.  This means that anything beyond an RA81 (or maybe RA82)
is is being throttled by the attachment...

Performance with the KDM70 should be better, and the board rumored to
support the RF series drives in the VAX6000 series should offer performance
similar to the DS5000 SCSI at far less cost than the HSC mess.  Why DEC
can't/won't implement a simple XMI/SCSI disk/tape adapter is a religious
matter best resolved by buying a Sun or other "open" system.

> I would like to find out if we are doing something wrong or if this
> is normal performance with the 5820.  Interresting that the DS5000 IO
> performance even with scsi drives appears to be faster than the 5820.

While we are generally statisfied with our 5810, I'd be hard put to
recommend the solution to anyone at the moment.  All the DEC rumors seem
to point to DECstation and DECsystem 5400 upgrades in the winds, without
a peep about the 5800 (except for the DEC ECL MIPS project cancelation,
which probably would have fit in the 5800 context).  Also, the basic
multi-processor support seems to be somewhat up in the air.

A cluster of DS5000's with with directly attached SCSI drives seems to
offer a hell of a lot better price/performance than the DS5800, plus
lower lower long term memory and disk expansion prices.  This could
change somewhat if DEC decides to deliver a new 5800 CPU board with some
MIPS or a memory board using 4M-bit chips, although if FDDI performance
is sufficiently impressive, "FDDI/NFS clustering" might be preferable
to multi-processor solutions.

> Again, since we just installed these machines ( about a month ago ), it could
> be related to setup.

If you are really distressed with the performance of you 5820, be sure
to notify your DEC salespersons of the fact in writing.  This should
get their attention and put you in a good barginning postion for an
alternate configuration, especially if you feel they recommended the
DS5820 over more cost effective alternatives or features such as
multi-processor capabilities that aren't delivering their full potential.

-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr at cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)