Oracle 10g RMAN Compression

If you have large databases and you use RMAN to back them up, and you are a little concerned with how much space they currently take up, this could be just the tool for you.

Previously, it was not possible to backup your database with RMAN and conserve space using compression; this had to be done afterwards using some third party software. However, from Oracle 10g onwards you now have the option to compress your backup set as it is being backed up. So, what’s the catch? Good question. And here are the answers:

  1. Increased time to back up the database. For example, I was backing up a 700GB database in around 1:20 minutes. With compression it took around 2:20.
  2. Increased CPU overhead. I was using an 8core, Itanium 2 server and the CPU was running at an average of 80%. It’s done out of hours, so it’s not a problem.

The result is good. The backup files are now only 20% of their original size, which makes them much more manageable.

The restoring of the files also takes longer. I haven’t  managed to work out exactly how much longer, because the server I’ve been using for the restore is constrained by CPU. It increases the load on the server when restoring as well.

I discovered an issues surrounding RMAN cumulative incremental backups which is definitely worth a read.

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Category: RMAN

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