什麼叫archive log expired?

A status of "expired" means that the backup piece or backup set is not found in the backup destination. With tape management systems, the automated tape library routines will expire files on the tape once a certain period of time has passed. RMAN uses this terminology to say that the tape management system has expired the file. It is no longer available. Therefore, the backup piece is expired as well.

A status of "obsolete" means the backup piece is still available, but it is no longer needed.

expired表明，備份片或備份集找不到了。在使用磁帶機的時代，自動執行的磁帶庫策略將會定期將磁帶上的檔案過期，RMAN使用了這種叫法。如果備份集或備份片過期了，表明備份集或備份片已經沒有了。如果我們執行crosscheck，檔案不存在的記錄將會被記錄為expired。

obsolete表明，備份片依然在，但是不在需要了。這個判斷依據是，我們在configure命令中設定的相關部分。比如我們設定我們的保留策略是redundancy2，表明我們保留2個備份，如果我們在做一個備份的話，最老的那個就成為obsolete，如果FRA滿了，obsolete狀態的backup可以被複寫。

**REF**

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https://neeraj-dba.blogspot.com/2011/08/difference-between-obsolete-and-expired.html