Path: utzoo!mnetor!uunet!husc6!cmcl2!nrl-cmf!ames!elroy!mahendo!jplgodo!wlbr!scgvaxd!trwrb!trwrc!agnew
From: agnew@trwrc.UUCP (R.A. Agnew)
Newsgroups: comp.sys.nsc.32k
Subject: Re: Streaming and other things (was Re: ulimit() broken on ICM systems)
Message-ID: <236@trwrc.UUCP>
Date: 5 Feb 88 19:10:17 GMT
References: <1558@mmm.UUCP> <976@nscpdc.NSC.COM> <325@gen1.UUCP>
Organization: TRW-MEAD, San Diego, Ca.
Lines: 22
Keywords: INFO-ICM ICM nsc
Summary: The real problem with SCSI tapes!

In article <325@gen1.UUCP> tyler@gen1.UUCP (Tyler IVANCO) writes:

>>In article <1558@mmm.UUCP> schultz@mmm.UUCP (John C Schultz) writes:
>>
>>>and the poor streaming capability of the tape drive.  I have asked Natl for
>>>a little help on these performance issuses which has resulted in a 
>>>resounding "thud".
>	The Sun 3/50 didn't stream until I used my little routine below.
>	I believe that this is a problem of the operating system getting
>in the way of the I/O from/to disk/tape.  On the UofT 4.2 port for the
>ICM, it is quite easy to stream the tape drive using tar with a large
>blocking size.  e.g.
>	tar cbf 1024 /dev/rmt4 .

Yes, this helps but it does not fix it. No, its not the operating system.
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. 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.