Oracle Rac
1. Architecture
解說：用戶發起請求到Application Server， Application Server（這裡可以理解為Bserver）。Application Server 會將數據庫連接請求發送至上圖兩個oracle db server。兩個Oracle Db Server背後共享同一份數據，這兩個db server同時對外提供服務，任意一個db server down機。原連接會轉發至另一存活的db server。數據通過光纖交換機，儲存到儲存介質。
數據庫可簡單理解為內存和儲存的組合，內存在db server中，數據在儲存介質中，如上圖ASM。如數據庫出現問題，基本也是內存或儲存問題。（這裡不考慮網絡故障）。如db主機故障，rac有多個實例，可以保證db服務不中斷。另一種顧慮，儲存出現故障，可以冗餘的儲存保證數據不丟失，如oracle的ASM,OCFS2,Raw devices等。
2. Windows Or Linux
Advantages of Oracle UNIX:
Significant performance improvement
Provides High Availability
Contains in-depth system utilities and open-source code
Highly respected by Oracle personnel
Advantages of Oracle Windows:
Very easy to deploy and support
Requires far less IT training
Simple interface to Microsoft tools such as ODBC and .NET.
In my personal opinion, here are some specific disadvantages to Linux and Windows:
Disadvantages of Oracle UNIX:
Required specialized skills (vi editor, shell scripting, etc.)
Required highly-technical Systems Administrators and DBA
Contains in-depth system utilities and open-source code
Security Holes (if mis-configured)
Susceptible to root kit attacks
Disadvantages of Oracle Windows:
Slower than Linux
Less glamorous for the SA and DBA
History of poor reliability (bad reputation)
Security Holes (if mis-configured)
Susceptible to Internet viruses
Link : Linux or Windows for Oracle?
注意： RAC並不是1+1=2. 即Rac性能，並不是隨著db server 數量成正比增加，如設置不當，性能比單實例還低的情況也很常見。
