Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!UCBVAX.BERKELEY.EDU!"Dan Karron
From: Dan Karron@UCBVAX.BERKELEY.EDU
Newsgroups: comp.sys.sgi
Subject: Re: Questions bru-ing
Message-ID: <9012220452.AA17500@karron.med.nyu.edu>
Date: 22 Dec 90 04:52:57 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: karron@cmcl2.nyu.edu
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Dave Olson write about what Peter S. Shenkin writes:

>I'm not clear on what you mean by 'recognize' here.  By default, bru
>uses the 'normal' method of doing multivolume tapes on IRIX (for the
>SCSI and and xm tape drives), which is to write until EOT is detected,
>then switch to a new volume. To do this, the tape sizes are set to 0K
>in /etc/brutab.  There is absolutely no way to determine tape lengths
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^HUH???
>ahead of time, since e.g. a QIC 150 drive could have either QIC150 or
>QIC120 cartridges, in any of several lengths.  This is true of most
>types of tape drives.  If you are certain of the capacity, and are sure
>you will use exactly the same tape type and length for each volume, you
>could use the -s option to specify the length, or edit /etc/brutab.
>
>| It is also a real pain that -e does not work with -Z;  the FM does not
>| mention this limitation; however, an attempt to do this elicits an error 
>| message.  I submit that just about the only time you need -e is when you use 
>| -Z;  yet that's when you can't get it.
>
>The reason it doesn't do this is that it would actually have to read and
>compress every single file in order to determine how much space the
>compressed files would require.  This is incredibly slow.  If you really
                                          ^^^^^^^^^^^^^^^SO WHAT!
>wanted to know, you could always do something gross like:
>	bru -cvfZ /dev/null .... | tail
>

Sounds like a good idea, actually. Since my tape backup is done automatically
from crontab in the dead of night after I leave, I don't really care how
slow it is. I mt ret the tape a number of time during the backup process
just for its good health. My main worry is the tape filling up and the
Night Backup script not knowing what to do. I compress the data to put off
the eventual EOT . I would like some foolproof
way to know in advance if I am goint to hit EOT, not blunder on it and
risk corrupting my backup. That way I can do something intelligent before
it happens!

We need a program to size any serial media (qic,dat, etc). I have seen it
on more business oriented computer systems (NCR unix). We also need
a taylored bru tab that know about sgi boxes (there are no entries for
sgi tape devices in the bru tab!) 


Cheers!

dan.
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