Oracle RMAN Backup of Read Only Plugged-In Tablespace

Oracle RMAN Backup Transport Tablespace  Limitations

Oracle RMAN backup of transportable tablespace has a number of limitations for Oracle 10g. Oracle Transportable Tablespace allow for the efficient movement of large volumes of data between Oracle databases. On the whole this works well and once setup is far more efficient data than processing through database links.

What probably is not widely known is that Oracle RMAN in Oracle Database 10gR2 seems to have some difficulty with backup of a plugged in read only tablespace (the default state for a tablespace that is plugged in using transport tablespace).

There are two issues with using Oracle RMAN for backup on 10g when you have plugged in read only tablespace’s that have not been set to read write:

• RMAN will not backup the datafile’s for the plugged in tablespace.
• RMAN will not report the datafile’s as part of the ‘report need backup’ or ‘restore database preview check read only’ commands either.

Reviewing the 10gR2 documentation set I could not find any reference to this limitation. In the 11gR1documentation the ability of RMAN to backup plugged in read only tablespace’s is listed as a new feature. As written in the documentation:

Backup of read-only transportable tablespace’s

In previous releases, RMAN could not back up transportable tablespace’s until they were made read/write at the destination database. Now RMAN can back up transportable tablespace’s when they are not read/write and restore these backups.

The Solution

If you are on 10g and use TTS but leave the plugged in tablespace as read only it might be worth validating at the datafile level exactly what is and is not backed up.

In the worst case if the plugged in tablespace has not been backed up then the following process should correct any gaps in the backup strategy:

1. Set read only tablespace to read write.
2. Set tablespace above back to read only.
3. Backup the tablespace after it has been set read only (Oracle will keep archivelogs until a tablespace that has been set RO has been backed up after the switch to RO).