Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!lll-winken!uunet!virtech!cpcahil
From: cpcahil@virtech.uucp (Conor P. Cahill)
Newsgroups: comp.unix.sysv386
Subject: Re: DPT controller?
Keywords: DPT disk controller
Message-ID: <1991May19.011411.24968@virtech.uucp>
Date: 19 May 91 01:14:11 GMT
References: <1991May14.235110.18644@tous.uucp> <1991May17.131717.26942@virtech.uucp> <31@metran.UUCP>
Distribution: na
Organization: Virtual Technologies Inc.
Lines: 61

jay@metran.UUCP (Jay Ts) writes:

 [ about the DPT format utility ]
>Am I correct in assuming that this is an MS-DOS utility that is shipped
>with the controller?

Yes.

>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?

The benefits of a caching controller apply to multi-users systems up
to a limit (after which the benefits start to dwindle until you get down
to performance equal to the non-caching controllers).

>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.

This really varies depending upon the implementation of the controller.
The two key factors in performance are:

   a) host-card data transfer interface. (Bus master DMA- best, programmed 
      i/o - worst, shared mem - somewhere in between)

   b) write-thru-cache - this is definately a looser when you consider 
      performance. 

>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.

In that case I would look at the DPT SCSI EISA cashing controller which 
*should* get you much better performance than the ESDI controller.  This
is because:

	1. the EISA controller uses bus-mastering DMA for very fast bus
	   transfers (the ISA controller uses programmed i/o) (this should
	   be a very big win)

	2. The SCSI controller can process multiple disk i/o operations 
	   to different drives simultaneously.

	3. the SCSI i/o bus has a greater bandwidth than the ESDI one.

Note: all this stuff on the EISA controller is heresay, I don't have one
in house (although my mouth waters every time I think about getting 
one :-}

One gauge of performance (and yes, I know it is not a hard number) is
that while I have a 33MHZ 386 with 16MB of ram and a SCSI controller
on my desktop, I do most of my work on the machine with the DPT 
because I like watching my compiles zoom.
-- 
Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.
uunet!virtech!cpcahil                           46030 Manekin Plaza, Suite 160
                                                Sterling, VA 22170