ADSM-L

Re: Easy ADSM?

2000-02-06 13:55:30
Subject: Re: Easy ADSM?
From: Eric Lindbeck <elindbec AT SCTCORP DOT COM>
Date: Sun, 6 Feb 2000 13:55:30 -0500
Many thanks to everyone for their great suggestions!  Just one
follow-up question:

In his reply, Steve Branch described the following situation:
"Say you have a  file that changes every day and you back it up every
day and maintain 3 backup copies (just an example). Initially you have
3 good copies.  Then the user does something stupid to mess up the
file. If the user calls you right then and asks you to restore  from
backup you will be ok. Suppose the user doesn't call you thinking all
will be better tomorrow. You backup the file that is no longer any
good and one of your good backup copies ages off the system. The
next day the user tries to fix the problem and still doesn't call.
Since the file timestamp got updated again today the corrupt file is
again backed up tonight and another of the good copies ages off. If
the same thing happens the following day you will have nothing but
corrupt copies of that file in ADSM."

Even maintaining an ambitious number of versions (5?, 10?, 20?) is not
enough to guarantee no data loss under the above circumstances.  It's
always possible that the file was corrupted on the day before your
oldest version was made.  As strange as it seems that users can work
with corrupt data and not even know it, I've seen it happen a number
of times.  In an extreme case, I had to go back over 2 months of
historical backups to find the last good version of a file.

In the 'old' way of doing things, I could keep 1 full backup per month
in storage indefinitely.  Then, I could just go to our safe (or
off-site provider) and pull the full backup from 2 months ago, merge
the tape catalogs into the db, query the db for the file, and do the
restore.  What is the *SM method for recovering data in this sort of
situation?

Thanks again!
Eric Lindbeck
SCT
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