Re: Incremental Backup and Change Block Tracking Questions

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
without BCT.
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

--
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