What is archived redo log failover?

What is archived redo log failover?

Rating:

In releases prior to Oracle9i, Recovery Manager (RMAN) only looked in the first archive destination for archived redo logs when backing them up. However, in Oracle9i, RMAN can perform archived redo log failover. In other words, RMAN can perform the following tasks:

If at least one redo log corresponding to a given log sequence and thread number is available in any of the archiving destinations, RMAN backs up the available redo log.

If there is a corrupt block in a redo log that RMAN is accessing, RMAN searches other archive destinations for a copy of the redo log without corrupt blocks.

RMAN always backs up only one copy out of the identical copies of each distinct archived redo log.

For example, if the archived redo logs corresponding to the log sequence numbers 25, 26, 27, and 28 are archived to two archive destinations (Disk1 and Disk2), the control file will contain the archived redo log records as follows:

Sequence	Filename
25	Disk1/Arch25.log
25	Disk2/Arch25.log
26	Disk1/Arch26.log
26	Disk2/Arch26.log
27	Disk1/Arch27.log
27	Disk2/Arch27.log
28	Disk1/Arch28.log
28	Disk2/Arch28.log

If, during the backup operation, Arch26.log and Arch28.log archived redo logs are missing from Disk1, RMAN can use the failover feature to back up the archived redo logs from Disk2 as follows:

Sequence	If RMAN searches for...	Then RMAN can find and back up...
25	Disk1/Arch25.log	Disk1/Arch25.log
26	Disk1/Arch26.log (missing)	Disk2/Arch26.log
27	Disk1/Arch27.log	Disk1/Arch27.log
28	Disk1/Arch28.log (missing)	Disk2/Arch28.log

Rating: