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Backing up to disk

We have a TB database on Sun Solaris 2.8 -- version 9.2.0.4. There are more than 50 tablespaces with more than 800 data files. Daily data loads are about 0.5 GB. We plan to use RMAN in conjunction with NetBackup to backup files to the tape destination. However, we could not backup the file directly to tape, and the real issue is we only have about 100 GB of disk space.

The only way to perform the backup is to backup data into a stage area first, and then push to tape, erase the files on disk, and do another backup, ..., iterate until all of the data is backed up. (I assume that RMAN will lose cross-checking capability on a file that is erased in disk, but what about in tape?) Things become complicated due to the space issue, particular for the first initial backup, and time issue, as well. From the testing I did, it will take more than 10 hours to backup 500 GB.

I'm thinking that to take the tablespace level backup, one by one, monthly level 0 backup, and level 1/2 cumulative backup in between. What is the best way for situation like this? Is there any way to speed up the backup time using RMAN?

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I have been in your situation before, and it is less than ideal. If you must backup to disk, and you do not have enough disk, then your solution is to perform tablespace backups, one by one. Once you have an entire database backed up, then you can switch to incremental backups. Depending on the nature of your transactions and the data that they change, you may or may not be able to peform an incremental of the entire database. Personally, I would either ask my management for more disk for your backups or I would ask for the ability to write RMAN directly to tape. I'm not as familiar with NetBackup. But I do know that both Legato and Veritas have an optional plug-in that lets RMAN communicate directly with tape devices managed by Legato or Veritas. We used the Legato version and it was great being able to backup RMAN backups directly to tape. And the software was not nearly as expensive as purchasing more disk.

This was first published in April 2005

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