Path: utzoo!yunexus!gen1!tyler
From: tyler@gen1.UUCP (Tyler IVANCO)
Newsgroups: comp.sys.nsc.32k
Subject: Re: Streaming and other things (was Re: ulimit() broken on ICM systems)
Keywords: ICM nsc Streaming Tapes
Message-ID: <326@gen1.UUCP>
Date: 7 Feb 88 16:00:21 GMT
Article-I.D.: gen1.326
Posted: Sun Feb  7 11:00:21 1988
References: <1558@mmm.UUCP> <976@nscpdc.NSC.COM> <325@gen1.UUCP> <236@trwrc.UUCP>
Reply-To: tyler@gen1.UUCP (Tyler IVANCO)
Organization: gen1 - York University, Petrie Bldg, Downsview, Ontario CANADA
Lines: 40


	With regards to my recent suggestion and commments regarding streaming,
In article <236@trwrc.UUCP> agnew@trwrc.UUCP (R.A. Agnew) writes:
>The real problem is that the brain damaged SCSI controllers that Sun and
>others used in those old designs did not support the full SCSI prrotocol
>and thus cannot release the bus to the CPU while the transport is in
>motion. 

	Yes, this is quite true; but I understand that SUN simply didn't
write drivers to support the SCSI disconnect command.  Perhaps this was
because SUN used a controller that didn't support that operation.  As a result 
the SUN SCSI bus cannot be used during a tape operation.  This effectively
hangs the workstation unless running programs off NFS.  However, you
can stream the write operation if all of your data is in memory.  

>This is the reason why you can't stream with them. Replacing the
>ACB2070 with a decent SCSI controller is part of the real answer.
>Note that the Sun3-50 can release and this feature is supported by Sun OS
>version 3.4.  The National board has a similar problem.

	I'm not sure that I agree with the assertion that the ICM has
a similar problem.  It may be that the 4.2 port does not support the
SCSI disconnect option, but at least one can still use the hard drive 
while tape operations are active, including large block writes.  The
emulex controllers suggested by NSC seem to support this mode.  You can,
from the monitor execute a SCSI copy direct tape to drive command and
dump the entire drive to tape without stopping (except of course for
track changes).  In this case the CPU is not involved in the transfer 
at all.  Indeed, a Z-80 is the only initiator on the bus.

	However,  if running through the CPU,  the OS and the
CPU would have to be very fast indeed in order to stream the tape
without blocking the data.   So from this point of view, the board
and the software are the problem.  

-- 
Phone: (416)736-2100 x7765                               Tyler Ivanco
Institute for Space and Terrestrial Sciences  - Solar/Terrestrial Physics Lab
BITNET: fs300022@yusol         UUCP: ...uunet!mnetor!yunexus!gen1!tyler
        yfcs0027@yorkvm1                    ...utzoo!/