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Re: rman compression

From: Ted Chyn <tedchyn_at_yahoo.com>
Date: 30 Aug 2001 10:53:59 -0700
Message-ID: <44a19320.0108300953.46d35b97@posting.google.com>


howard, thnx for the reply. If I have a table with 500mb under hwm 500mb will be backup by rman even when most records were deleted ?

thnx again.

"Howard J. Rogers" <howardjr_at_www.com> wrote in message news:<3b8e22a3$1_at_news.iprimus.com.au>...
> The Backup and Recovery Course not being quite so popular as it used to be
> (and can't you just tell from some of the posts here of late?!), I may be a
> bit out of touch with RMAN... but here goes for nothing...
>
> RMAN doesn't "compress" backups, if by "compression" you're thinking of
> anything like WinZip or gzip.
>
> Being an Oracle utility, however, it is intelligent enough to realise when a
> block on disk has never been used (ie, is above a high watermark somewhere),
> and will not include such blocks in the output backup sets. That contrasts,
> of course, with O/S backups which, not having a clue what they are actually
> copying, take a byte for byte copy of the physical datafile, unused blocks
> and all. Net result: RMAN backup sets are significantly smaller than a
> physical backup simply using O/S copy commands would be.
>
> RMAN makes things even smaller when you do incremental level backups: again,
> because it understands Oracle blocks and data structures, it can tell
> whether a block has changed since the last backup... if it has, it gets
> included in the backup set. If not, it doesn't -and once again, such
> omission makes the resultant backup set much smaller than it otherwise would
> be.
>
> If there is actually an RMAN command to compress a backup set a la WinZip,
> I'm not aware of it, and frankly I'd be gobsmacked ...Oracle generally takes
> the view that you play around with compression utilities at your peril.
> It's valuable data, after all.
>
> Regards
> HJR
>
>
>
> "Ted Chyn" <ericis6_at_home.com> wrote in message
> news:Bhlj7.139845$oh1.55982353_at_news2.rdc2.tx.home.com...
> > sir, Can anybody shed light on how rman compress the datafile during
> backup
> > ?
> > thnx ted chyn
> >
> >
Received on Thu Aug 30 2001 - 12:53:59 CDT

Original text of this message

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