Google File System (GFS) is a proprietary distributed file system developed by Google for its own use. [1]
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Design
GFS is optimized for Google's core data storage needs, web searching, which can generate enormous amounts of data that needs to be retained;[2] Google File System grew out of an earlier Google effort, "BigFiles", developed by Larry Page and Sergey Brin in the early days of Google, while it was still located in Stanford.[2] The data is stored persistently, in very large, even multiple gigabyte-sized files which are only extremely rarely deleted, overwritten, or shrunk; files are usually appended to or read. It is also designed and optimized to run on Google's computing clusters, the nodes of which consist of cheap, "commodity" computers, which means precautions must be taken against the high failure rate of individual nodes and the subsequent data loss. Other design decisions select for high data throughputs, even when it comes at the cost of latency. The nodes are divided into two types: Master nodes and Chunkservers. Chunkservers store the data files, with each individual file broken up into fixed size chunks (hence the name) of about 64 megabytes,[3] similar to clusters or sectors in regular file systems. Each chunk is assigned a unique 64-bit label, and logical mappings of files to constituent chunks are maintained. Each chunk is replicated a fixed number of times throughout the network, the default being three, but even more for high demand files like executables. The Master server doesn't usually store the actual chunks, but rather all the metadata associated with the chunks, such as the tables mapping the 64-bit labels to chunk locations and the files they make up, the locations of the copies of the chunks, what processes are reading or writing to a particular chunk, or taking a "snapshot" of the chunk pursuant to replicating it (usually at the instigation of the Master server, when, due to node failures, the number of copies of a chunk has fallen beneath the set number). All this metadata is kept current by the Master server periodically receiving updates from each chunk server ("Heart-beat messages"). Permissions for operations are handled by a system of time-limited, expiring "leases", where the Master server grants permission to a process for a finite period of time during which no other process will be granted permission by the Master server to access the chunk. The modified chunkserver, which is always the primary chunk holder, then propagates the changes to the chunkservers with the backup copies. The changes are not saved until all chunkservers acknowledge, thus guaranteeing the completion and atomicity of the operation. Programs access the chunks by first querying the Master server for the locations of the desired chunks; if the chunks are not being operated on (if there are no outstanding leases), the Master replies with the locations, and the program then contacts and receives the data from the chunkserver directly (similar to Kazaa and its supernodes).
See also
- BigTable
- MapReduce
- Fossil, the native file system of Plan 9
- List of Google products
- Hadoop and its "Hadoop Distributed File System" (HDFS), an open source Java product similar to GFS.
- Cloud storage
References
| This article or section needs sources or references that appear in reliable, third-party publications. Primary sources and sources affiliated with the subject of this article generally are not sufficient for a Wikipedia article. Please include more appropriate citations from reliable sources, or discuss the issue on the talk page. This article has been tagged since November 2007. |
- ^ a b "All this analysis requires a lot of storage. Even back at Stanford, the Web document repository alone was up to 148 gigabytes, reduced to 54 gigabytes through file compression, and the total storage required, including the indexes and link database, was about 109 gigabytes. That may not sound like much today, when you can buy a Dell laptop with a 120-gigabyte hard drive, but in the late 1990s commodity PC hard drives maxed out at about 10 gigabytes." "How Google Works".
- ^ "The files managed by the system typically range from 100 megabytes to several gigabytes. So, to manage disk space efficiently, the GFS organizes data into 64-megabyte "chunks," which are roughly analogous to the "blocks" on a conventional file system--the smallest unit of data the system is designed to support. For comparison, a typical Linux block size is 4,096 bytes. It's the difference between making each block big enough to store a few pages of text, versus several fat shelves full of books." "How Google Works"
- "The Google File System" (PDF), Sanjay Ghemawat, Howard Gobioff, and Shun-Tak Leung; pub. 19th ACM Symposium on Operating Systems Principles, Lake George, NY, October, 2003.
External links
- A Google published research paper about GFS
- Google File System Eval: Part I at StorageMojo
- "How Google Works"
- ZDnet article on GFS
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