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From: olson@anchor.esd.sgi.com (Dave Olson)
Newsgroups: comp.sys.sgi
Subject: Re: Questions bru-ing in my mind
Message-ID: <1990Dec21.174239.11753@odin.corp.sgi.com>
Date: 21 Dec 90 17:42:39 GMT
References: <1990Dec18.211216.24299@cunixf.cc.columbia.edu>
Sender: news@odin.corp.sgi.com (Net News)
Organization: Silicon Graphics, Inc.  Mountain View, CA
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In <1990Dec18.211216.24299@cunixf.cc.columbia.edu> shenkin@cunixf.cc.columbia.edu (Peter S. Shenkin) writes:
| 1.  Backup all files in a directory EXCEPT the ones I list;  for example,
|     all of /usr except /usr/src and /usr/people.  I know I can make a list
|     of the files I want in a file, then use 'bru -c - < filename', but then
|     I have to create this file again everytime I do a backup, since I do
|     not expect the contents of /usr to be static.

It is relatively rare to want to back up a whole directory tree except
for a few files, so none of the standard backup programs provided with
IRIX have this capablity.  Generating the filelist as above is the only
way.

| 2.  Recognize either a specified or the default tape drive using the -e
|     option.  The FM says that with -e, "If the media size is unknown or
|     unspecified it is assumed to be infinite."  In fact, it always seems
|     to assume it is infinite, even if specified.  The FM also says that 
|     /dev/tape is used as the default, so my reading says that -e should 
|     assume this default; however, even if I say 'bru -e -f /dev/tape', bru 
|     still assumes the media size is infinite.  Without any -f option, 'bru -x' 
|     does in fact seem to know how long a tape is, so why doesn't 'bru -e',
|     and why can't it figure this out even with -f?

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
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
wanted to know, you could always do something gross like:
	bru -cvfZ /dev/null .... | tail

I agree that the above issues should be clarified in the man page.  It
will be fixed in the next release.

--

	Dave Olson

Life would be so much easier if we could just look at the source code.