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Monday, January 30, 2012

How Web giants store big - and we mean big - data
Credit: Arstechnica
Consider the tech it takes to back the search box on Google's home page: behind the algorithms, the cached search terms, and the other features that spring to life as you type in a query sits a data store that essentially contains a full-text snapshot of most of the Web. While you and thousands of other people are simultaneously submitting searches, that snapshot is constantly being updated with a firehose of changes. At the same time, the data is being processed by thousands of individual server processes, each doing everything from figuring out which contextual ads you will be served to determining in what order to cough up search results.
The storage system backing Google's search engine has to be able to serve millions of data reads and writes daily from thousands of individual processes running on thousands of servers, can almost never be down for a backup or maintenance, and has to perpetually grow to accommodate the ever-expanding number of pages added by Google's Web-crawling robots. In total, Google processes over 20 petabytes of data per day.
That's not something that Google could pull off with an off-the-shelf storage architecture. And the same goes for other Web and cloud computing giants running hyper-scale data centers, such as Amazon and Facebook. While most data centers have addressed scaling up storage by adding more disk capacity on a storage area network, more storage servers, and often more database servers, these approaches fail to scale because of performance constraints in a cloud environment. In the cloud, there can be potentially thousands of active users of data at any moment, and the data being read and written at any given moment reaches into the thousands of terabytes.

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