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Re: Backup trends (2): HOT or COLD

From: JEDIDIAH <jedi_at_nomad.mishnet>
Date: 9 Apr 2004 14:29:28 -0400
Message-ID: <slrnc7dqj9.3b4.jedi@nomad.mishnet>

On 2004-04-03, Howard J. Rogers <> wrote:
> "Bob Jones" <email_at_me.not> wrote in message
> news:LDnbc.23629$
>> "Sybrand Bakker" <> wrote in message
>> > On Fri, 2 Apr 2004 07:37:30 +0000 (UTC), Lucyna Witkowska
>> > <> wrote:
> It is true. RMAN does an intelligent read of Oracle blocks and then an
> intelligent write. That's good because it understands the concept of an
> Oracle block, so yes it skips any that are empty. It does that
> automatically. Optionally, it also does something which no O/S script has a
> hope in hell of pulling off: namely, comparing the age of an Oracle block
> with the age of the same block in a prior backup, and if the two are the
> same, skipping the block. That, of course, is the basis for an incremental
> backup. At the Oracle block level. And in 9i, RMAN can recover at the block
> level too.
> So yes, it has lots of nice features. But those are merely incidental to the
> real reason why you should use RMAN in preference to O/S scripts:
> performance. RMAN doesn't cause the database to generate 20 or 30 times the
> amount of redo per transaction that O/S hot backups do. RMAN doesn't hammer

Certainly a valid point.

> one data file to death before moving on to another, but instead multiplexes
> across many datafiles, little bits being taken from each one in turn. RMAN

This is a just a simple coding and configuration issue. If you take our korn coding as seriously as the rest of your DBA duties, this should never be a problem.

> parallelises in a way no O/S script never could. And you can throttle the
> I/O rate up or down for RMAN to minimise the impact on the production
> database or to maximise the speed at which the backup is done.

Any of this can be crudely estimated using less complicated tools.

> RMAN doesn't require maintenance if datafiles are added, either, so I'm not
> sure what the point of mentioning that was.

The original comparison was likely to some really shoddy scripts.


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Received on Fri Apr 09 2004 - 13:29:28 CDT

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