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Tom Kyte

Thanks for the question, Roland.

Asked: June 04, 2008 - 1:46 pm UTC

Last updated: November 02, 2011 - 12:07 pm UTC

Version: 9.2.0

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You Asked

Hello Tom,
I'm about to change our backup strategy. I have taken classic hot backups in the past and want to use RMAN now. My manager asked me if there is a possibility to precalculate/predict the size of an RMAN backup without the need to take an RMAN backup, level 0 and especially an incremental backup.

I appreciate your help.

Best regards,
Roland

and Tom said...

Not that I am aware of, it would be extremely problematic given null block compression, optimized undo backup (new in 11g) and other compression features. About the best you can say is "it will be less than or about equal to the size of the database"

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Size reduction using compression

Kev, November 02, 2011 - 10:50 am UTC

Is there a way of calculating how much space could be saved using RMAN compression in 10g and 11g? We have some quite large datafiles that are backed up locally on each server and are then copied over to our Data Protection Manager (DPM) servers for storage. The problem is the size of the files that must be copied over and the bandwidth that is available to us.

Many thank in advance!
Tom Kyte
November 02, 2011 - 12:07 pm UTC

it totally depends on the nature of the data.

a datafile full of gif's stored in lobs - probably near 0%
a datafile full of "all work and no play makes jack a dull boy" - many times compression.

I would suggest 'benchmarking' it with your data - your mileage will vary.

Thank you!

Kev, November 04, 2011 - 6:47 am UTC

My job for next week then! Thank you for your time!
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