ADSM-L

Re: The "incremental forever" paradigm, Was: How would you do thi s?

1998-03-06 12:52:40
Subject: Re: The "incremental forever" paradigm, Was: How would you do thi s?
From: Hilton Tina <HiltonT AT TCE DOT COM>
Date: Fri, 6 Mar 1998 12:52:40 -0500
But the backup stgpool to a copypool is incremental in nature.  The
first time you issue the command, it will copy everything.  The next
time you issue it, it will only copy the new stuff.  It doesn't replace
everything.  So, the first time you run it, it will copy 51GB to the
copypool.  If you run it daily, and an additional 10GB was backed up,
the next day only 10GB will be added to the copypool.

Is there something I've missed?  Or did you believe it would copy 51GB
every time you issue backup stgpool?

Tina Hilton
Thomson Consumer Electronics

        ----------
        From:  John Schneider[SMTP:jdschn AT ibm DOT net]
        Sent:  Friday, March 06, 1998 12:05 PM
        To:  ADSM-L AT VM.MARIST DOT EDU
        Subject:  The "incremental forever" paradigm, Was: How would you
do this?

        Curtis J. Pogue wrote:
        >
        > My company wants to do a full backup every month and
incrementals in
        > between.  I've argued with them about not needing full backups
but
        > they just say "That's the way we've always done it!".  Any
way, I
        > going to either use the absolute value in the backup copy
group or
        > specify selective in the backup schedule.  My question is
should I
        > create a separate policy domain and every thing that goes with
it for
        > the monthly backups?
        >
        > TIA
        Curtis,
                I waited until replies to your post stopped trickling in
before
        I posted.
                My problem with the "incremental forever" paradigm is
that
        it assumes that once you write a file to a disk or tape you can
just
        forget about it, the backup has been done.  There is no need to
ever
        back up that same file twice, even years later.
                That just seems completely ridiculous.
                What about a bad tape?  Have none of you ever had that
happen?
        What about a operator loosing a tape, or the tape being sent
offsite
        and being lost by the offsite provider?  Or a tape being dropped
by
        the operator and the case broken.  This is reality.  No media is
        impervious to problems, that's why we back up to begin with.
                And the problem doesn't go away if you use disk instead
of tape
        either.  Disks fail, too, and at the most inopportune moments.
And we
        do not have the disk space available to support disk pools,
anyway.
                It just seems too optimistic to presume that one copy of
all your
        critical files would be enough, no matter what.
                Also, the idea of backing up a storage pool to a copy
storage
        pool sounds good to me, but seems to be exceedingly slow.  We
have
        about 51GB worth of active data, and after I did some
measurements it
        looks like it would take over 10 hours of dedicated time to do
the
        tape-to-tape copy.  It would be easier if we could do that in 1
or 2
        hour chunks spread out over a week.  I have looked in to using
"export
        node" to do this, but that is not really a good substitute,
since you
        would have to reimport the entire node again to restore
anything.
                Please explain to this novice why, on the one hand, we
        implement a backup strategy to cover the possibility of loosing
disks,
        be we ignore the possibility of the backup media itself going
bad?

        Best Regards,
        John Schneider


***********************************************************************
        * John D. Schneider     * Email: jdschn AT ibm DOT net * Phone:
314-349-4556 *
        * Lowery Systems, Inc.
***********************************************
        * 275 Axminister        * Disclaimer: Opinions expressed here
are mine*
        * Fenton, MO 63026      * and mine alone.  My company is off the
hook.*

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