RE: Incremental Backup and Change Block Tracking Questions

From: Luca Canali <>
Date: Fri, 22 Feb 2008 17:33:45 +0100
Message-ID: <>

  1. We have been using BCT on 10g for a while now and also performed a few restores, including production DBs, without any problems (yet).
  2. I have only used RMAN compression in a test environment and I was not happy with it. It was using a lot of CPU with the result that the backup speed dropped down considerably (the backup was CPU bound on the DB server). I am going to try this again when I have faster CPUs. Also 11g has some interesting new features to reduce CPU usage with compression, but I digress.
  3. BCT makes a huge difference when doing incremental backups. If you have large TBS with little transactional activity on them you can backup very quickly even multi TB DBs (tested). For incremental strategies longer than 8 incremental backups we also tune _bct_bitmaps_per_file (default 8)


[] On Behalf Of Sam Bootsma Sent: Friday, February 22, 2008 4:53 PM
Subject: Incremental Backup and Change Block Tracking Questions

Hello all,  

Oracle, Enterprise Edition, on AIX 5.3.  

I am preparing to change our RMAN backups to use Incremental Backups and Change Block Tracking. I am also considering to use compression. But first I have a few questions that I hope you can assist with.  

  1. Have you found Incremental backups and Change Block Tracking to be reliable; i.e, can you reliably backup and then restore and recover?
  2. What about Oracle compression during an RMAN backup? Is that reliable?
  3. How much of a performance hit using the Change Block Tracking feature? What about Oracle compression?
  4. Do you know if any of these features are additional cost? Do you know if there is a view in Oracle that outlines what features come with EE and what features are additional cost?
  5. We also have the option to do compression at the tape drive level. Is anybody aware of any reason that Oracle compression (during backup) would be better or worse than letting the tape drive do it?
  6. I have read that restores of a cumulative backup a generally faster than restores of a differential backup. What makes cumulative faster? Is it simply that RMAN will just one incremental file to restore and recover from (plus archive logs)? If there are six differential backups to recover from, RMAN should be able to restore and recover the six files without DBA intervention. I don't see a significant time difference. Perhaps a couple minutes extra because it has six more files to deal with?

Thanks for your input!  

Sam Bootsma

Oracle Database Administrator

Information Technology Services
George Brown College

Phone: 416-415-5000 x4933
Fax: 416-415-4836
E-mail: <>  

Received on Fri Feb 22 2008 - 10:33:45 CST

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