| Lesson 7 || Open database backup options |
| Objective || Explain the options for tablespace backups. |
Oracle Open Database Backup
Backup Datafiles for Tablespace
One of the advantages of open database backup is its flexibility. A DBA can choose to backup all datafiles for a tablespace or just one datafile for that tablespace. An additional advantage is that the database remains accessible during the backup process. Tablespace and datafile backups should only be performed when the database is operating in ARCHIVELOG mode. Such backups cannot be used to restore a database running in NOARCHIVELOG mode.
Backing up a tablespace
It is important to frequently back up tablespaces with rollback segments and tablespaces that contain important data such as system data. Tablespaces containing only temporary segments do not need to be backed up.
Backing up an individual datafile
One reason a DBA may choose to frequently backup the datafiles of extensively used tablespaces is to reduce database recovery time.
If recovery is required and a more recent copy of the datafile is used to restore the damaged one, the amount of time a datafile remains in "Fuzzy" state is minimized.
Because of this, fewer archived redo logs need to be applied to the restored datafiles to roll them forward to the time of the failure.
FUZZY Backup Problem
The "Fuzzy" backup problem often appears during the process of an open database backup. For example, let us say a situation arises
where the operating system backup starts at the beginning of the datafile and midway through the copy operation, a change occurs with bytes
behind the read/write head. Bytes behind the head are missed but are vital to the change. The resulting imperfect copy must be recovered using the Redo Logs in use at the time of the backup. The following SlideShow demonstrates the Fuzzy problem in an open database backup.