1、If one of the online redo log members is lost,the status in v$logfie will be INVALID
2、If the contents of the redo log file are incomplete ,the status of the file in the V$LOGFILE view will be STALE
3、You are using RMAN to perform backup and recovery on your database.The backup of one of the files was lost because it was located on a failed media.If you use CROSSCHECK command to verify the existence of the backup,the statues of this bakcup will be updated to EXPIRED
4、The status will be updated to OBSOLETE when the bakcup becomes older than the retention policy specified for the database.
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