Veritas Quick I/O and Cached Quick I/O

BTxigua發表於2009-03-19
UI

1、什麼是Quick I/O and Cached Quick I/O？

VERITAS Quick I/O is a special feature of the VERITAS File System (VxFS) for the VERITAS Database
Edition for Oracle.  The Database Edition is an integrated suite of system software enhancements and
configuration guidelines that combine to help system administrators and database administors configure
Oracle database servers.

VERITAS Quick I/O provides a raw device interface to regular files created under VxFS.  It bypasses
certain file system overhead operations (i.e. locking layer) and supports kernel asynchronous I/O (KAIO),
hence Quick I/O provides the benefits of both file system manageability and raw device performance.
Cached Quick I/O is an enhancement to Quick I/O that enables Oracle DBAs to utilize their large system
memories more effectively.

傳統的檔案系統，由於對檔案的single write lock存在，導致檔案系統在併發環境中讀寫效率比較低。而裸裝置則不存在這個問題。Quick I/O其實就是消除了單寫鎖，提高檔案系統的效率。

Cached Quick I/O是對Quick I/O的一種增強處理，核心的思想就是不斷的記錄訪問的檔案的頻度，將最熱的檔案放在cache中，提高cache的命中率，從而提高檔案系統的效率。

可以簡單的理解這兩個特性：

1）Quick I/O解決的是傳統的unix檔案系統的single write lock問題。

2）Cached Quick I/O解決的是cache的命中率問題。

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/10867315/viewspace-571524/，如需轉載，請註明出處，否則將追究法律責任。

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