FastDFS 原理介绍

FastDFS is an open source high performance distributed file system (DFS). It's major functions include: file storing, file syncing and file accessing, and design for high capacity and load balancing.

 

 

<!--EndFragment-->

Introduction

FastDFS is an open source high performance distributed file system. It's major functions include: file storing, file syncing and file accessing (file uploading and file downloading), and it can resolve the high capacity and load balancing problem. FastDFS should meet the requirement of the website whose service based on files such as photo sharing site and vidio sharing site.

 

FastDFS是一个开源的分布式文件系统，她对文件进行管理，功能包括：文件存储、文件同步、文件访问（文件上传、文件下载）等，解决了大容量存储和负载均衡的问题。特别适合以文件为载体的在线服务，如相册网站、视频网站等等。

<!--EndFragment-->

Details

FastDFS has two roles: tracker and storage. The tracker takes charge of scheduling and load balancing for file access. The storage store files and it's function is file management including: file storing, file syncing, providing file access interface. It also manage the meta data which are attributes representing as key value pair of the file. For example: width=1024, the key is "width" and the value is "1024".

 

FastDFS服务端有两个角色：跟踪器（tracker）和存储节点（storage）。跟踪器主要做调度工作，在访问上起负载均衡的作用。存储节点存储文件，完成文件管理的所有功能：存储、同步和提供存取接口，FastDFS同时对文件的meta data进行管理。所谓文件的meta data就是文件的相关属性，以键值对（key value pair）方式表示，如：width=1024，其中的key为width，value为1024。文件meta data是文件属性列表，可以包含多个键值对。

 

The architecture of FastDFS:

 

FastDFS的架构：

 

 

 

The tracker and storage contain one or more servers. The servers in the tracker or storage cluster can be added to or removed from the cluster by any time without affecting the online services. The servers in the tracker cluster are peer to peer.

 

The storarge servers organizing by the file volume/group to obtain high capacity. The storage system contains one or more volumes whose files are independent among these volumes. The capacity of the whole storage system equals to the sum of all volumes' capacity. A file volume contains one or more storage servers whose files are same among these servers. The servers in a file volume backup each other, and all these servers are load balancing. When adding a storage server to a volume, files already existing in this volume are replicated to this new server automatically, and when this replication done, system will switch this server online to providing storage services. When the whole storage capacity is insufficiency, you can add one or more volumes to expand the storage capacity. To do this, you need to add one or mone storage servers.

The identification of a file is composed of two parts: the volume name and the file name.

 

 跟踪器和存储节点都可以由一台多台服务器构成。跟踪器和存储节点中的服务器均可以随时增加或下线而不会影响线上服务。其中跟踪器中的所有服务器都是对等的，可以根据服务器的压力情况随时增加或减少。

为了支持大容量，存储节点（服务器）采用了分卷（或分组）的组织方式。存储系统由一个或多个卷组成，卷与卷之间的文件是相互独立的，所有卷 的文件容量累加就是整个存储系统中的文件容量。一个卷可以由一台或多台存储服务器组成，一个卷下的存储服务器中的文件都是相同的，卷中的多台存储服务器起 到了冗余备份和负载均衡的作用。

在卷中增加服务器时，同步已有的文件由系统自动完成，同步完成后，系统自动将新增服务器切换到线上提供服务。

当存储空间不足或即将耗尽时，可以动态添加卷。只需要增加一台或多台服务器，并将它们配置为一个新的卷，这样就扩大了存储系统的容量。
FastDFS中的文件标识分为两个部分：卷名和文件名，二者缺一不可。

 

 

The file upload flow:

 

 1. client询问tracker上传到的storage，不需要附加参数；
 2. tracker返回一台可用的storage；
 3. client直接和storage通讯完成文件上传。

 

 

 

The file download flow:

 

 

 1. client询问tracker下载文件的storage，参数为文件标识（组名和文件名）；
 2. tracker返回一台可用的storage；
 3. client直接和storage通讯完成文件下载。