RE: Incremental Backup and Change Block Tracking Questions

  • From: "Luca Canali" <Luca.Canali@xxxxxxx>
  • To: <sbootsma@xxxxxxxxxxxxxx>
  • Date: Fri, 22 Feb 2008 17:33:45 +0100

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)


From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Sam Bootsma
Sent: Friday, February 22, 2008 4:53 PM
To: oracle-l@xxxxxxxxxxxxx
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


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: sbootsma@xxxxxxxxxxxxxx <mailto:sbootsma@xxxxxxxxxxxxxx> 



Other related posts: