Sias,

the snapshot *does not* clear the log. It is a snapshot, not a backup. Its
goal is to make copy of the DB without touching the Full+Incremental+Log
chain.
Look at the Administrator's Guide:
"A snapshot database backup is a full database backup that does not
interrupt the current full and incremental backup series. "

Zlatko Krastev
IT Consultant






Sias Dealy <hnre AT UREACH DOT COM>
Sent by: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
13.03.2003 18:25
Please respond to hnre


        To:     ADSM-L AT VM.MARIST DOT EDU
        cc:
        Subject:        Re: Database backup strategy?


Matt,

In my shop, we do full backups of the TSM database. That is
because the TSM database will fit on one tape. When the TSM
database span across two tapes, then we will be thinking about
doing incremental backup of the database. Keep in mind that you
can only do so many incremental backup of the database. Once
you reach that limit, a full backup of the database need to be
done.

If TSM was doing a full backup twice a day. I would suspect,
the reason on why two backups are done is to keep the recovery
log from over committing. That is if TSM is in rollforward mode.

Must be nice to have a remote disaster recovery site that is
less than a 5-minute walk.  ;)

Sias


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---- On    , Matt Simpson (matt AT UKY DOT EDU) wrote:

> I'm curious about the type and frequency of database backups
that
> people do.  I've inherited a TSM environment set up by
sombeody else
> and I'm trying to make sense out of it.
>
> The original setup did two backups every day, a full and a
snapshot.
> The full stayed onsite and the snapshot went offsite.  (We
use DRM,
> and the MOVE DRM * SOURCE=DBS sent the snapshot offsite and
left the
> full alone).  That seemed like overkill, so I changed
the "onsite"
> backup to do a full backup on Sunday and an incremental other
days.
> But at two hours for a full backup, and almost as long for an
> incremental, I'm wondering if we're still spending more time
than
> necessary backing up our database.  Does anybody else see the
need
> for two daily backups?  I think the likeliihood of a disaster
> requiring a database restore is so slim that a single offsite
copy
> might be enough, especially since our "offsite vault" is less
than a
> 5-minute walk (which raises another issue, but thats what
we're
> living with).
>
> Does anybody mess with full/incremental database backups? Or,
if I'm
> only going to do one backup a day, would it make more sense
to do a
> full every day, to simplify things if I do have a disaster
and need
> to restore?
> --
>
>
> Matt Simpson --  OS/390 Support
> 219 McVey Hall  -- (859) 257-2900 x300
> University Of Kentucky, Lexington, KY 40506
> <mailto:matt AT uky DOT edu>
> mainframe --   An obsolete device still used by thousands of
obsolete
> companies serving billions of obsolete customers and making
huge obsolete
> profits for their obsolete shareholders.  And this year's run
twice as fast
> as last year's.
>
>