270.632356105 ENABLED 11599872
SQL>
Backup Compression
As you learned earlier in this chapter, we can either configure backup compression as the default
for backupsets or explicitly specify compression in an RMAN backup command (for the purposes
of this example, the backup was performed on September 3, 2007):
RMAN> backup as compressed backupset database;
452 Oracle Database 11g DBA Handbook
Comparing the size of the actual datafiles with the backupset, we can see just how much
compression we can achieve for some additional CPU overhead:
ASMCMD> cd +DATA
ASMCMD> du DW
Used_MB Mirror_used_MB
2675 5361
ASMCMD> cd +RECOV/dw/backupset
ASMCMD> ls
2007_08_25/
2007_08_29/
2007_08_30/
2007_09_03/
ASMCMD> du 2007_09_03
Used_MB Mirror_used_MB
241 483
ASMCMD>
The database files occupy about 2.7GB in the +DATA disk group; the compressed backupset
from RMAN comes in at 241MB, which is well over a 90 percent compression rate.
Using a Flash Recovery Area
Earlier in this chapter, we covered the initialization parameters required to set up the flash recovery
area: DB_RECOVERY_FILE_DEST and DB_RECOVERY_FILE_DEST_SIZE. Both of these parameters
are dynamic, allowing the DBA to change either the RMAN destination for backups or the amount
of space allowed for backups in the flash recovery area without restarting the instance.
To facilitate a completely disk-based recovery scenario, the flash recovery area should be big
enough for a copy of all datafiles, incremental backup files, online redo logs, archived redo logs
not on tape, control file autobackups, and SPFILE backups.
Pages:
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695