RMAN Backup Question - FILESPERSET
- From: "Mark Strickland" <strickland.mark@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 24 Jan 2007 16:16:22 -0800
Oracle 10.1.0.5 on Solaris 9. Using block change tracking file and
flash_recovery_area.
The incremental level 1 backups of one of our databases produce a large
number of very small backupsets, about 20K each. This causes the backup of
the flash_recovery_area to tape to take around 4-1/2 hours whereas the
backup to the flash_recovery_area beforehand takes around 15 minutes. There
are 378 datafiles and many of them never get modified (old partitions). The
backupsets appear to always have 3-4 datafiles and the backupsets for those
never-modified files are very small. FILESPERSET is not set, but MAXSETSIZE
is set to 6000M. There are four channels. I've pored over the manuals and
Robert Freeman's fine RMAN book, along with Metalink and Google, and it
seems there is conflicting information about the default value for
FILESPERSET. In one place in the docs, it says that
"The number of files to be backed up is divided by the number of channels.
If the result is less than 64, then it is the number of files placed in each
backupset. Otherwise, 64 files will be placed in each backupset."
Robert Freeman appears to agree with that. In my case that would be the
lesser of 378/4 or 64, so 64. In other places in the docs, it says that the
default maximum number of files that will go into a backupset is 4. That
pretty much matches what I'm seeing in my environment. I've been
experimenting with FILESPERSET today in a test environment and I'm able to
set it to different values and observe that the backupsets do contain that
many files. Therefore, on Friday evening, I plan to change FILESPERSET to
64 in Production and run the incremental level 1 backup and see what
happens. If it fails for some reason, I can easily re-run it with the
default.
Another oddity is that for our level 0 backups, we have MAXSETSIZE set to
10G but I see a few backupsets that exceed that size, like 20G. Not worried
about that, just curious.
Any insights?
Regards,
Mark Strickland
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