Fail-Fast
維基百科地址：http://en.wikipedia.org/wiki/Fail-fast
Fail-fast is a property of a system or module with respect to its response to failures. A fail-fast system is designed to immediately report at its interface anyfailure or condition that is likely to lead to failure. Fail-fast systems are usually designed to stop normal operation rather than attempt to continue a possibly flawed process. Such designs often check the system’s state at several points in an operation, so any failures can be detected early. A fail-fast module passes the responsibility for handling errors, but not detecting them, to the next-higher system design level.
從字面含義看就是“快速失敗”，儘可能的發現系統中的錯誤，使系統能夠按照事先設定好的錯誤的流程執行，對應的方式是“fault-tolerant（錯誤容忍）”。以JAVA集合（Collection）的快速失敗爲例，當多個線程對同一個集合的內容進行操作時，就可能會產生fail-fast事件。例如：當某一個線程A通過iterator去遍歷某集合的過程中，若該集合的內容被其他線程所改變了；那麼線程A訪問集合時，就會拋出ConcurrentModificationException異常（發現錯誤執行設定好的錯誤的流程），產生fail-fast事件。
Fail-Over
維基百科地址：http://en.wikipedia.org/wiki/Failover
In computing, failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application,[1] server, system, hardware component, or network. Failover and switchover are essentially the same operation, except that failover is automatic and usually operates without warning, while switchover requires human intervention.
Fail-Over的含義爲“失效轉移”，是一種備份操作模式，當主要組件異常時，其功能轉移到備份組件。其要點在於有主有備，且主故障時備可啓用，並設置爲主。如Mysql的雙Master模式，當正在使用的Master出現故障時，可以拿備Master做主使用。
Faile-Safe
維基百科地址：http://en.wikipedia.org/wiki/Fail-safe
A fail-safe or fail-secure device is one that, in the event of failure, responds in a way that will cause no harm, or at least a minimum of harm, to other devices or danger to personnel.
Fail-Safe的含義爲“失效安全”，即使在故障的情況下也不會造成傷害或者儘量減少傷害。維基百科上一個形象的例子是紅綠燈的“衝突監測模塊”當監測到錯誤或者衝突的信號時會將十字路口的紅綠燈變爲閃爍錯誤模式，而不是全部顯示爲綠燈。
另外就是我們誤用的“自動功能降級”翻譯做“Auto-Degrade”會更好一些。
Fail-Back
Fail-over之後的自動恢復，在簇網絡系統（有兩臺或多臺服務器互聯的網絡）中，由於要某臺服務器進行維修，需要網絡資源和服務暫時重定向到備用系統。在此之後將網絡資源和服務器恢復爲由原始主機提供的過程，稱爲自動恢復。
參考地址：
http://weibo.com/p/1001603773524304121727
http://xiemingmei.iteye.com/blog/2128094