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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.unix.wizards
Subject: Re: On backups
Message-ID: <8050@utzoo.UUCP>
Date: Tue, 19-May-87 19:38:23 EDT
Article-I.D.: utzoo.8050
Posted: Tue May 19 19:38:23 1987
Date-Received: Tue, 19-May-87 19:38:23 EDT
References: <7272@brl-adm.ARPA>
Organization: U of Toronto Zoology
Lines: 21

> 	The disadvantages may be more subtile: Do I lose anything by
> not bringing the system down to single user level for the full dumps?

In general, there is no way to be absolutely certain you have got a clean
backup unless you take the system down, because otherwise you are trying
to get a snapshot of a moving target.  For example, if a database system
is active while you are doing backups, there is a significant chance that
the database files on your backup are not in a consistent state.  This can
be true even if the backup copies of individual files are perfect snapshots,
which is not easy to guarantee.

On the other hand, if the system is quiet and the dump program is a bit
conservative, you'll get something that is *close* to clean, possibly
good enough.

When I started running utzoo, I put my foot down, after too many experiences
with bad backups (n.b. modern backup programs are better):  we do *all* our
backups single-user.
-- 
"The average nutritional value    Henry Spencer @ U of Toronto Zoology
of promises is roughly zero."     {allegra,ihnp4,decvax,pyramid}!utzoo!henry