Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!ames!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (System Mangler)
Newsgroups: comp.periphs
Subject: Re: Fast Tape drives
Message-ID: <2626@cit-vax.Caltech.Edu>
Date: Fri, 8-May-87 22:26:43 EDT
Article-I.D.: cit-vax.2626
Posted: Fri May  8 22:26:43 1987
Date-Received: Sun, 10-May-87 01:14:12 EDT
References: <43735@beno.seismo.CSS.GOV>
Organization: California Institute of Technology
Lines: 21
Summary: A trick for streamers

In article <43735@beno.seismo.CSS.GOV>, mo@seismo.CSS.GOV (Mike O'Dell) writes:
> if you every use the tapedrive for anything besides
> dumps, like really writing tapes full of data,
> the speed of the drive matters even more since
> you probably aren't writing the gargantuan blocks
> that dump uses to get its efficiency.

On the TU80, if you simply buffer enough write data for at least
15 writes and then do them in a tight loop, the TU80 streams in
high-speed mode for those writes, and repositions once while you
crunch another large chunk of data.  You don't need gargantuan
writes, although you do need a reasonable-sized buffer (100KB or so).

>   you can come pretty close quite often [to running it full speed]

My SI 9900 disk controller isn't able to keep even a 1600-bpi drive
moving at full speed.  Whenever dump hits a clump of small files,
the controller is 90+% busy, and the tape pauses a lot.  What kind
of disk controller do you use?!?

Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck