备份恢复技术论述.ppt

BACKUP Command Options During the backup operation, an Oracle Database process computes a checksum for each block to detect corruption. RMAN verifies the checksum when restoring the copy. This is referred to as physical corruption detection. You can use the NOCHECKSUM option to suppress the checksum operation and speed up the backup process. If the database is already maintaining block checksums, then this option has no effect. You can use the CHECK LOGICAL option to test data and index blocks that pass physical corruption checks for logical corruption, for example, corruption of a row piece or index entry. If logical corruption is detected, the block is logged in the alert log and trace file of the server process. You can set a threshold for the allowed number of logical and physical corruptions with the MAXCORRUPT parameter. As long as the sum of physical and logical corruptions that is detected for a file remain below this value, the RMAN backup operation completes and Oracle Database populates the V$DATABASE_BLOCK_CORRUPTION view with the corrupt block ranges. If MAXCORRUPT is exceeded, then the operation terminates without populating the view. You can use the VALIDATE option to check for physical and logical errors in database files. When using the BACKUP command with the VALIDATE option, RMAN scans the specified files and verifies their contents, testing whether this file can be backed up. This command does not actually backup up the specified files. Archived Redo Log File Backup Sets A common problem experienced by DBAs is not knowing whether an archived log has been completely copied out to the archive log destination before attempting to back it up. Recovery Manager has access to control file or recovery catalog information, so it knows which logs have been archived and can be restored during recovery. You can back up archived redo log files with the BACKUP ARCHIVELOG command or include them when backing up data files and control files with the BACKUP … PL