Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!ll-xn!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (System Mangler)
Newsgroups: comp.unix.wizards
Subject: Re: On backups
Message-ID: <2651@cit-vax.Caltech.Edu>
Date: Mon, 11-May-87 06:06:51 EDT
Article-I.D.: cit-vax.2651
Posted: Mon May 11 06:06:51 1987
Date-Received: Wed, 13-May-87 01:07:01 EDT
References: <7272@brl-adm.ARPA>
Organization: California Institute of Technology
Lines: 22
Summary: disk-to-disk backups have their risks

In article <7272@brl-adm.ARPA>, lewis@cel.fmc.COM (Bil Lewis) writes:
> Incrementals: At 2am, each machine tars up all the new user files
> (ignoring .o, .psf, .tmp, ... files) and ships them to the Eagle where
> they are kept for a month.

> Do I lose any security by having the incrementals on-line?  [I think
> not.	It requires TWO simultanious head crashes to lose anything & I've
> never head of such a thing.]

Some consultants here did their backups by periodically copying the
active disk pack to a backup pack.  One night, the active pack crashed
in the middle of a backup.  They were left with half of an image copy
of the filesystem, which is completely useless; they lost the entire
sources and compilers for their proprietary operating system.  A year
later, they are still stuck with making binary patches.

So it doesn't require two simultaneous head crashes to lose a lot.

Think about what will happen if your disk controller goes nuts.
(My experience is that this is more likely than an Eagle crash).

Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck