This is to ensure that Oracle will always recover over the datafile contents with redo entries. The current SCNs are recorded in redo, but not in the datafile. Thus, only half of the total storage space is. This is also why the SCN of the datafile header does not change when a tablespace enters hot backup mode. RAID 1 (which requires at least two drives) uses double the number of drives necessary to store the information. What if the OS copy pulls half a block, and while that is happening, the block is changed by DBWR? When the OS copy pulls the second half of the block it will result in mismatched halves, which Oracle would not know how to reconcile Because the OS (usually) reads blocks at a different rate than Oracle, your OS copy will pull pieces of an Oracle block at a time. This is to avoid fractured blockĪ block fracture occurs when a block is being read by the backup, and being written to at the same time by DBWR. The corresponding datafiles header will be freezed i.e CKPT process will not update latest SCNīody of the datafile is still active i.e DBWRn will write the dirty blocks to datafilesĪfter end backup, datafile header will be unfreezed and CKPT process will update latest SCN immediately by taking that information from controlfilesĭuring hot backup, we will observe much redo generated because oracle will copy entire data block as redo entry into LBC. ![]() Whenever we place a tablespace or database in begin backup mode, following happens Therefore, after a backup job starts, if parts of data are changed before being copied, the changed. Under this backup mode, data will just be simply copied to the backup device by order until the end. Taking the backup while the database is up and running is called hot backupĭuring hot backup database will be in fuzzy state and still users can perform transactions which makes backup inconsistent Inconsistent backup means to back up files when an application is still up and running, which is also called hot backup.
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