For an online backup, do you need to put tablespaces hot backup mode when using RMAN?
To understand why RMAN does not require extra logging or backup mode, you must first understand why those features are required for non-RMAN online backups. A non-RMAN online backup consists of a non-Oracle tool, such as cp or dd, backing up a datafile at the same time that DBWR is updating the file. We can’t prevent the tool from reading a particular block at the exact same time that DBWR is updating that block. When that happens, the non-Oracle tool might read a block in a half-updated state, so that the block which is copied to the backup media might only have been updated in its first half, while the second half contains older data. This is called a “fractured block”. If this backup needs to be restored later, and that block needs to be recovered, recovery will fail because that block is not usable. The ‘alter tablespace begin backup’ command is our solution for the fractured block problem. When a tablespace is in backup mode, and a change is made to a data block, instead of loggin
