AshFS: 一個支援離線操作的輕量化行動檔案系統

Abstract

隨著網際網路的蓬勃發展，有愈來愈多的服務都力求和網路結合，為數眾多的行動裝置如手機和PDA等也開始強調其連網能力，以求達到機動性。在這種情況下，許許多多的網路檔案系統也發展了起來，讓在網路另一端的使用者，可以像在操作本地端檔案一般，透明化的存取遠端電腦上的檔案。以往許多的網路檔案系統，都是針對高頻寬網路環境設計的，常預設使用者擁有一個穩定且高速的網路連線，然而這假設對於到處漫遊的行動網路使用者來說並無法完全適用。行動網路有著不穩定的連接性，以及變動性極大的頻寬；而這些檔案系統並無法自動處理這類的狀況，一旦與伺服器失去連結就無法繼續使用。少數支援離線操作的檔案系統，由於是針對大型分散式環境所設計的，相對來說比較耗資源，且花費了較多對使用者來說很有限的網路頻寬。在本論文中，我們設計了一個適用於個人的行動檔案系統-- AshFS，希望能更讓移動使用者，透過其行動裝置透明的存取自己個人電腦裡的檔案，並且不受外在網路環境變動的影響。AshFS支援離線操作和自動同步，能在網路斷線的情況下繼續使用，並且在恢復連線後主動同步客戶端和伺服器之間的檔案；此外，它也能有效的節省頻寬的使用。□了驗證我們設計的理念，在論文的最後我們設計了一連串的實驗。實驗結果顯示AshFS有著較高操作速度和較低的頻寬使用量，並且在網路環境變動的情況下，其效能也能維持在一定的水準。

Because of the pervasion of Internet, a large number of devices combined with Internet to enhance their functionalities. Under this background, many network file systems have been developed to allow people accessing files located on the remote host. Traditional network file systems usually assume that users have strong and steady connections. However this assumption is rarely true for the mobile users because of the unpredictable connectivity and widely-varying bandwidth of the mobile networks. Although some of previous works can function correctly in this circumstance, they are designed for larger distributed environments, and they consume too much bandwidth, which is very restricted for the mobile users. In this thesis, we describe the designs and implementations of a personal mobile file system, AshFS, which can mount users’ personal computers as a part of their devices’ local filesystem and can deal with the unsteady network status automatically. AshFS supports some advanced features including disconnected operations and automatic synchronization. Since AshFS is designed for the personal use, we simplify some complex mechanisms used in distributed file systems before. And this also reduces a user’s bandwidth consuming and resource usage. In the end we set up a series of experiments. The experiments show that AshFS has a higher operation speed and a lower protocol overhead. In addition, the variation of the network status doesn’t influence AshFS’s performance much.