Re: Incremental Backup and Change Block Tracking Questions
Date: Fri, 22 Feb 2008 09:43:41 -0800
On Fri, Feb 22, 2008 at 7:52 AM, Sam Bootsma <sbootsma_at_georgebrown.ca> wrote:
> 1. Have you found Incremental backups and Change Block Tracking to be
> reliable; i.e, can you reliably backup and then restore and recover?
> Incremental level 1 backups with BCT are much faster than level 1's
Restore is not a problem.
Level 1 backups are a very good thing.
Let's say you took a level 0 yesterday.
Last night a batch job loaded a table in direct path mode, which will not appear in the archive logs.
Today you do a level 1 incremental.
The blocks loaded in direct path mode will be backed up by the level 1, as they are recorded in the BCT.
So in the event of recovery, the level 1 backup not only skips all the archive logs from the end of the level 0 to the beginning of the level 1, the table loaded with direct path will also be recovered, which would not have happened with the level 0 + archive logs.
> 2. What about Oracle compression during an RMAN backup? Is that reliable?
Haven't heard any problems of reliability. You may want to test it however, as
my tests have shown quite a CPU hit.
> 3. How much of a performance hit using the Change Block Tracking feature?
> What about Oracle compression?
< 1% according to Oracle. I haven't measured the actual CPU usage of compression, only
its effect on a running database.
> 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?
> Can't answer that.
> 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?
Tape level compression is probably faster. A problem there might differing implementations
of the compression between different versions of tape firmware. Might be a problem if you
need to restore old tapes with new hardware.
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?
Haven't tested it, don't know.
-- Jared Still Certifiable Oracle DBA and Part Time Perl Evangelist -- http://www.freelists.org/webpage/oracle-lReceived on Fri Feb 22 2008 - 11:43:41 CST