DPT controller?

[Jay Ts]

In article <1991May17.131717.26942 at virtech.uucp>, cpcahil at virtech.uucp (Conor P. Cahill) writes:
> rbt at tous.uucp (Robert B. Tate) writes:
> 
> >I am planning to install a DPT SmartCache (ESDI) disk controller with 4.5
> >megs of cache this weekend (with a PRIAM ID330-E (model 638) 338Meg
> >Does anyone know _anything_ I sould know?
> 
> 1. Each disk drive must be formatted by the DPT formatter (even if you already
>    formatted it with another formatter).

Am I correct in assuming that this is an MS-DOS utility that is shipped
with the controller?

> >FYI: 
> >Under MS-DOS, the disk & controller look VERY fast! (I hope it is as fast
> >under UNIX. When TOUS is baching up outgoing news, it takes for *ever*
> 
> It is very fast under unix also (until you fill up the cache, then it 
> is about average).  In other words, compiles or processing news screams,
> but a dd from /dev/rdsk/0s0 to /dev/null is actually slightly slower than
> the same command on a system with a WD1007 ESDI controller. 

This is starting to sound interesting.  Is this based on a single-user
UNIX system, or does it apply to multi-user systems as well?

I have been wondering under what conditions the DPT and other caching disk
controllers are really effective enough to be worth the extra price and
administration complexities.  I have been under the impression that as
long as the system is serving a number of users, and has a fair amount of
main memory (8-16 Mb) for UNIX's disk buffers, the extra speed from the
cache on the controller is only about 10-15%, even if it is maxed out at
4 Mb.

My own interests are in systems with very fast processors (33 MHz 386, or
25 MHz or faster 486) and a large number of users to support, i.e., systems
whose performance is limited not by the CPU but by disk throughput.

Any comments?  I would like to hear from those who have direct experience
with the DPT or other caching controller, and have been able to compare
against similar systems with no caching controller.  I would really like
some cold, hard numbers, but on usenet, I suppose that may be asking too
much :-)

Jay Ts, Director
Metran Technology
uunet!pdn!tscs!metran!jay