Path: utzoo!utgpu!water!watmath!mks!wheels
From: wheels@mks.UUCP (Gerry Wheeler)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ARC Wars
Message-ID: <507@mks.UUCP>
Date: 19 Sep 88 20:59:56 GMT
References: <1653@dataio.Data-IO.COM> <360004@hpbsla.HP.COM>
Organization: Mortice Kern Systems, Waterloo, Ont.
Lines: 37

In article <360004@hpbsla.HP.COM>, campbell@hpbsla.HP.COM (gary campbell) writes:
> I would like an archiver with compression that can handle multi-floppy
> archives, primarily as a means of system backup.

Something which fits that description is the cpio utility in the MKS
Toolkit.  It is not, however, freeware.

On Unix, one would use a command like "find /usr | cpio -ocv | compress
>/dev/xxx".  On DOS, of course, because there are no real pipes, the
entire output of cpio would be saved in a temp file before compress was
run.  This doesn't work well if you are trying to back up 10 megs of
data.  :-) So, we added an option to cpio to have it do the compression
on the fly.  The results are the same as above, but no pipe is involved. 

Our cpio will also assume that a write error indicates a full disk, and
asks if you want to continue on another volume.  This allows the cpio
file occupy as many floppies as necessary. 

> Someone on a local BBS made the following comments about compression in
> a backup utility:  "Also, you would have to wonder about the integrity
> of the backed-up files.  If the archive dropped one bit -- it could
> destroy multiple files within the one archive.".

True.  You don't want to use compression if your floppies are flakey. 
(But who would use flakey floppies for backup?) If you're going to start
from scratch and create a backup program with compression, you probably
want to compress each file separately and try to arrange some way to
re-synchronize to the headers within the file in case there is some
corruption.  Possibly the use of a separate file with pointers into the
backup file would work.  Or, perhaps the indexes could be stored at the
end of the file in a fixed size area.  (Not too handy on a multi-volume
backup, though.)
-- 
     Gerry Wheeler                           Phone: (519)884-2251
Mortice Kern Systems Inc.               UUCP: uunet!watmath!mks!wheels
   35 King St. North                             BIX: join mks
Waterloo, Ontario  N2J 2W9                  CompuServe: 73260,1043