ADSM-L

Re: <no subject> -- Becomes backup vs archive

1998-12-23 12:02:53
Subject: Re: <no subject> -- Becomes backup vs archive
From: "Kelly J. Lipp" <lipp AT STORSOL DOT COM>
Date: Wed, 23 Dec 1998 10:02:53 -0700
Well, sort of.

You not only specify the number of versions to keep (verexists), but how
long to keep each of these versions (retextra).  So, using verexists and
retextra, you specify exactly how long to keep a particular backed up
version of a file.  After retextra days, the extra versions of the file are
expired.  The backup copy of the file that exists on the client (the active
version) is maintained as long as the file continues to exist on the
client.  If that file is deleted on the client, then the backup copy on the
server is marked inactive.  If this is the only remaining copy of the file
on the server, it is maintained for retonly days.

So, if you set these four parameters correctly for your environment, it is
possible for you to offer the ability to restore data back to any point in
time.

By default, ADSM sets these values at:

verexists       2
retextra                30
verdeleted      1
retonly         60.

So, if a file changes everyday for two weeks, you can still only recover
that file back two days.  This is not what most users of backup tools have
come to expect.  In GFS environments, incremental tapes are usually kept
for 30-40 days and then recycled.  As it turns out then, 30-40 days is the
guaranteed retrieval period that can be offered.  As a practical matter,
most files reside on a system longer than a single day, perhaps across a
weekend boundary, and are, therefore, on a weekend full tape as well.  In
this case it MAY be possible to restore older data.  But, you can't
guarantee it.

We work with our customers to understand what their restoration
requirements are for each data type.  For restoration requirements less
than 180 days, we use backup.  For restoration requirements greater than
that, we develop archival procedures to accommodate them.

As most of you know, I've written a white paper discussing the differences
between backup and archive.  For a copy, email me off the list and I'll
send it on to you.

Thanks, and a very Merry Christmas, Happy Hanukah, or season's greetings to
all of you.

Kelly Lipp
Storage Solutions Specialists, Inc.
lipp AT storsol DOT com
www.storsol.com
(719) 531-5926

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