NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/unix/admin/4309

Text File | 1992-07-24 | 3.0 KB | 80 lines

Newsgroups: comp.unix.admin
Path: sparky!uunet!decwrl!access.usask.ca!kakwa.ucs.ualberta.ca!news
From: [e-mail] (Sherwood Botsford)
Subject: Re: multiple dumps on EXB-8200 8mm tape
Message-ID: <[e-mail]>
Sender: [e-mail]
Nntp-Posting-Host: fenris.space.ualberta.ca
Organization: University Of Alberta, Edmonton Canada
References: <[e-mail]>
Distribution: usa
Date: Fri, 24 Jul 1992 18:15:53 GMT
Lines: 66

Bill Heiser writes
>
> The problem I have is that when I write a tapefile to the non-rewinding
> device, and then write another file, when I try to read the files I seem
> to have to skip filemarks sometimes.  For example:  If I write a tape on
> a SunOS 4.1.1_U1 or 4.0.3 system, I have a tape with several tapefiles.
> If I try to read the tape by doing several consecutive 'restore' commands
> on the non-rewinding device, the restores after the first one fail -- unless
> I do a restore, then a "mt -f fsf 1".  So basically I seem to be getting
> extra file marks!

This one threw me for a loop initially.
The file mark is not (usually) explicitly written by the program, but is
written by the computer on closing the file.  It will aslo be done by the tape
if the previous command was write data, and the the current command is any tape
movement command.

Now, a filemark on either exabyte or DAT drives has a front and back side.
Front being on the Beginning of Tape side.

Any command that writes to the tape, finishes with a write filemark, and
leaves the head on the back side of the mark, ready to write the next file.

Any command that reads the tape leaves the tape positioned on the BOT side of
the file mark.

mt fsf's and bsf's behave this way too.  A bsf leaves the tape on the front
edge of the filemakr, and an fsf leaves it on the back.

So if you kill an operation, and want to reposition the tape to start it again,
you must do this:
mt bsf 1
mt fsf 1


In terms of your problem with the other machine, it may automatically put an
fsf after a read finishes.

I do modify my scripts behaviour for different machines with an environment
variable.  Since they are different drivers, I use that.

e.g.
#!/usr/local/bin/perl
..
$TAPE = $ENV{TAPE};
if  ("$TAPE" eq ""); { # No device defined.
  print "TAPE is not defined in your environment.\n";
  &Finish
  }
if  ("$TAPE" eq "/dev/nrxt0"); { &ExabyteSetup; }
if  ("$TAPE" eq "/dev/nrst0"); { &HPDatSetup;}
print "\tUsing tape device $TAPE \n";


Then in the various setup you can define a command string that is null for the
machine that doesn't need it, and does an mt fsf 1 for the machine that does
need it.

You could also do this by host name, host type, etc.

Hope this helps.

---
=> Sherwood Botsford                   [e-mail] <=
=> University of Alberta         Lab Manager, Space Physics Group <=
=> tel:[phone]                             fax: [phone] <=