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Home -> Community -> Mailing Lists -> Oracle-L -> RE: rman backup to disk, mismatch in amount backed up to each cha nnel
From: DENNIS WILLIAMS
Sent: Friday, October 22, 2004 9:12 AM
To: 'Peter.Hitchman_at_thomson.com'
Subject: RE: rman backup to disk, mismatch in amount backed up to each
channel
Peter - I could only speculate on why RMAN would shunt more backup to one filesystem than the other. I don't think you can control it anyway. We had a similar situation where we didn't have enough total free space on one device for the entire backup, and so wanted to split the backup between two devices. However, one device didn't have much free space so we wanted less of the back to go to that device. What I did was create two channels on the device where I wanted more of the backup to go, and only one channel on the other device. This worked very well. My suggestion would be to try that approach.
Dennis Williams
DBA
Lifetouch, Inc.
-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Hitchman, Peter
Sent: Friday, October 22, 2004 7:09 AM
To: oracle-l_at_freelists.org
Subject: rman backup to disk, mismatch in amount backed up to each channel
Hi,
We back up an Oracle 8.1.7.4 database to disk using rman. Its about 900 Gb.
It does work, but we find that much more data is getting sent to one channel
than the other. So when its done, one filesystem is over 50% full and the
other is only at 25%. I thought that rman automatically evened out the work
done by each channel and that would result in an even (ish) amount of disk
space being used in each filesystem.
What we want is for the amount written to each channel to be about even, that way we can do a backup and then rename the directories the backup is in before we run another one, in case the next backup fails for some reason. We only two file systems available (and we had to beg for these) and managed to get enough space in each in theory to hold two disk backups. But its no good if one of the filesystems goes over 50% with the first backup, because it means the next one will fail because of lack of disk space.
Does anyone know how we can control rman's behaviour in this case? (By the way, for reasons that are beyond me, it is not possible to change the disk space allocation so that the one of the filesystems is 25% bigger that the other).
Here is the rman script:-
connect target 'xxx/xxx_at_XXX';
connect catalog 'xxx/xxx_at_XXX';
run {
allocate channel t1 type disk format '/rman1/backup/cms.%U';
allocate channel t2 type disk format '/rman2/backup/cms.%U';
set limit channel t1 kbytes 10000000;
set limit channel t2 kbytes 10000000;
set command id to 'rman_backup';
backup
incremental level 0 cumulative
skip readonly
skip offline
database;
sql 'alter system archive log current';
change archivelog all crosscheck;
backup
filesperset 64
(archivelog all);
backup
current controlfile
tag = ctrlfile_level0backup;
release channel t1;
release channel t2;
change archivelog all crosscheck;
}
Thanks
Pete
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