From: zxmsd01@mailserv.zdv.uni-tuebingen.de (Gunther Schadow)
Subject: Re: tar 'multivolume' bugs and workaround workound
Organization: Comp. Center (ZDV) U of Tuebingen, FRG
Date: Tue, 1 Sep 1992 12:08:09 GMT

I think it is most desirable to have a tar with a kind of -z option
(say -Z) which does compress each file *before* dumping it into the
archive. This method would be superior against just compressing the
output stream of tar, what the -z option actually does. Yet it is
harder to realize.  
  The -z option can easily be simulated by a pipe: "tar -cf - whatever
|compress >medium". -z and -M wont work together anyway in the current
GNU tar. But the -Z option I am thinking of, is not realizable with a
simple shell scipt. You cannot just say something like "tar -cf medium
(compress whatever)".
  To compress every file on your disk before archiving it is no
solution, because (1) it takes time, (2) you have to uncompress
afterwards and (3) the access time will be modified, so you lose
information.
  I think it is *urgently* necessary to invent such a -Z feature into
GNU tar. The reason why this should be done is at hand: Say, you have
a backup of 30 disks. If this is one huge compressed tar archive, and
you loose one disk for whatever reason, you can forget about getting a
single correct file back from the disks beyond that deficient disk,
because uncompress gets completely out of sync. Why should you make
any backup then, if you cannot rely on it in case of emergency? It is
far more possible, that there is one out of 30 disks damaged -- what
about number 3 :-( -- than your 120 MByte HardDisk will crash over
years.
  GNU tar is abel to skip over damaged records and can even start
untarring from any point within the tar file, but only tar is, not
uncompress. This feature of GNU tar is also useful if you don't want
to spend half an hour playing disk jockey while uncompress|tar skips
over 25 disks until it extracts the 20kByte file you want in a few
seconds. Or even worse you made a type mistake in the file name you
give to tar, or you forgot the actual path to it: Again 30 minutes of
your live...
  Is there anybody who backed up his 240MBytes disk in 240 floppy disk
with the normal dump? Or made an extremely unreliable .tar.Z backup
onto approx 180 disks? I didn't --- and I cross my fingers :-). The
only backup I have is the Network; not that I had the facility to dump
to an NFS, but I publish almost every good changes I made to 386BSD
files onto agate.berkeley.edu.
  Nice to have a tape, but can you afford to pay $50 for a 40MByte
small cardridge of tape, if you need 6 of them for your level-0 dump?
BTW: Has anybody tried to use a video taperecorder to dump his HD onto
a cheap $2.5 videotape? This, together with a tar -Z facility would be
the most convenient, cheap, secure, just effective way of archiving
backup's or etc01 distributions.
  These are just a few of my thoughts about backups, archives, and
tar. I tried once to get into the tar sources to invent my -Z option,
but I failed due to the complexity of tar's method, and mainly due to
my lack of time. If there is anybody familiar with tar code, please
think about my -Z ideas, and help GNU tar to become the best common
archiving program!

regards
-Gunther
--
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Gunther Schadow,	          e-mail: Gunther@mailserv.ZDV.Uni-Tuebingen.DE
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7400 Tuebingen, Germany.__________Stop__________Horn Please!__________O.K. TATA