Server farm

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Server farm

A server farm or server cluster is a collection of computer servers – usually maintained by an organization to supply server functionality far beyond the capability of a single machine. Server farms often consist of thousands of computers which require a large amount of power to run and to keep cool. At the optimum performance level, a server farm has enormous costs (both financial and environmental) associated with it. Server farms often have backup servers, which can take over the function of primary servers in the event of a primary-server failure. Server farms are typically collocated with the network switches and/or routers which enable communication between the different parts of the cluster and the users of the cluster. Server farmers typically mount the computers, routers, power supplies, and related electronics on 19-inch racks in a server room or data center.

Server farms are commonly used for cluster computing. Many modern supercomputers comprise giant server farms of high-speed processors connected by either Gigabit Ethernet or custom interconnects such as Infiniband or Myrinet. Web hosting is a common use of a server farm; such a system is sometimes collectively referred to as a web farm. Other uses of server farms include scientific simulations (such as computational fluid dynamics) and the rendering of 3D computer generated imagery (also see render farm).

Server farms are increasingly being used instead of or in addition to mainframe computers by large enterprises, although server farms do not yet reach the same reliability levels as mainframes. Because of the sheer number of computers in large server farms, the failure of an individual machine is a commonplace event, and the management of large server farms needs to take this into account by providing support for redundancy, automatic failover, and rapid reconfiguration of the server cluster.

The performance of the largest server farms (thousands of processors and up) is typically limited by the performance of the data center’s cooling systems and the total electricity cost rather than by the performance of the processors. Computers in server farms run 24/7 and consume large amounts of electricity, for this reason, the critical design parameter for both large and continuous systems tends to be performance per watt rather than cost of peak performance or (peak performance / (unit * initial cost)). Also, for high availability systems that must run 24/7 (unlike supercomputers that can be power-cycled to demand, and also tend to run at much higher utilizations), there is more attention placed on power saving features such as variable clock-speed and the ability to turn off both computer parts, processor parts, and entire computers (WoL and virtualization) according to demand without bringing down services.

Performance per watt

The EEMBC EnergyBench, SPECpower, and the Transaction Processing Performance Council TPC-Energy are benchmarks designed to predict performance per watt in a server farm. The power used by each rack of equipment can be measured at the power distribution unit. Some servers include power tracking hardware so the people running the server farm can measure the power used by each server. The power used by the entire server farm may be reported in terms of power usage effectiveness or data center infrastructure efficiency.

According to some estimates, for every 100 watts spent on running the servers, roughly another 50 watts is needed to cool them. For this reason, the siting of a Server Farm can be as important as processor selection in achieving power efficiency. Iceland, which has a cold climate all year as well as cheap and carbon-neutral geothermal electricity supply, is building its first major server farm hosting site. Fibre optic cables are being laid from Iceland to North America and Europe to enable companies there to locate their servers in Iceland. Other countries with favorable conditions, such as Canada, Finland, Sweden and Switzerland, are trying to attract cloud computing data centers. In these countries, heat from the servers can be cheaply vented or used to help heat buildings, thus reducing the energy consumption of conventional heaters. 99bandar

Spam in blogs

Spam in blogs (also called simply blog spam, comment spam, or social spam) is a form of spamdexing. (Note that blogspam also has another meaning, namely the post of a blogger who creates posts that have no added value to them in order to submit them to other sites.) It is done by posting (usually automatically) random comments, copying material from elsewhere that is not original, or promoting commercial services to blogs, wikis, guestbooks, or other publicly accessible online discussion boards. Any web application that accepts and displays hyperlinks submitted by visitors may be a target.

Adding links that point to the spammer’s web site artificially increases the site’s search engine ranking on those where the popularity of the URL contributes to its implied value, an example algorithm would be the PageRank algorithm as used by Google Search. An increased ranking often results in the spammer’s commercial site being listed ahead of other sites for certain searches, increasing the number of potential visitors and paying customers.

This type of spam originally appeared in Internet guestbooks, where spammers repeatedly filled a guestbook with links to their own site and with no relevant comment, to increase search engine rankings. If an actual comment is given it is often just “cool page”, “nice website”, or keywords of the spammed link.

In 2003, spammers began to take advantage of the open nature of comments in the blogging software like Movable Type by repeatedly placing comments to various blog posts that provided nothing more than a link to the spammer’s commercial web site. Jay Allen created a free plugin, called MT-BlackList, for the Movable Type weblog tool (versions prior to 3.2) that attempted to alleviate this problem. Many blogging packages now have methods of preventing or reducing the effect of blog spam built in due to its prevalence, although spammers too have developed tools to circumvent them. Many spammers use special blog spamming tools like trackback submitter to bypass comment spam protection on popular blogging systems like Movable Type, WordPress, and others.

Other phrases typically used in the comment content can be stolen comments from other websites, “nice article”, something about their imaginary friends, plagiarised parts from books, unfinished sentences, nonsense words (usually to defeat a minimum comment length restriction) or the same link repeated.

Application-specific implementations

Particularly popular software products such as Movable Type and MediaWiki have developed or included anti-spam measures, as spammers focus more attention on targeting those platforms due to their prevalence on the Internet. Whitelists and blacklists that prevent certain IPs from posting, or that prevent people from posting content that matches certain filters, are common defences although most software tends to use a combination of the variety of different techniques documented below.

The goal in every potential solution is to allow legitimate users to continue to comment (and often even add links to their comments, as that is considered by some to be a valuable aspect of any comments section when the links are relevant or related to the article or content) whilst preventing all link spam or irrelevant comments from ever being viewable to the site’s owner and visitors.