Thursday, March 25, 2010
Friday, December 4, 2009
virtual private server
The physical server boots normally. It then runs a program that boots each virtual server within a virtualization environment (similar to an emulator). The virtual servers have no direct access to hardware and are usually booted from a disk image.
There are two kinds of virtualizations: software based and hardware based. In a software based virtualization environment, the virtual machines share the same kernel and actually require the main node's resources. This kind of virtualization normally has many benefits in a web hosting environment because of quota incrementing and decrementing in real time with no need of restarting the node. The main examples arexen, Virtuosso, Vserver , and open vz (which is the open source and development version of Parallels Virtuozzo Containers).
In a hardware based virtualization, the virtualization mechanism partitions the real hardware resources. In typical implementations, no burst and/or realtime quota modification is possible; the limits are hard and can only be modified by restarting a virtual machine instance[]. This kind of environment is potentially more secure in the sense that it is less subject to "Quality of Service crosstalk" between VM instances]; on the other hand, its security is typically dependent on the correctness of a larger and more complicated Trusted Computing Base[It is more commonly used in enterprise/commercial deployments[Examples include Microsoft Virtual Server, Virtuozo ,VMware ESX server, and xen
Clustered hosting
Clustered hosting is a type of that web hosting spreads the load of hosting across multiple physical machines ("nodes"), increasing availability and decreasing the chances of one service (for example FTP, or email) affecting another - for example web or database (e.g. MySQL). Many large websites run on clustered hosting solutions, for example, large discussion forums will tend to run using multiple front-end webservers with multiple back-end database servers.
Typically, most hosting infrastructures are based on the paradigm of using a single physical machine to host multiple hosted services, including web, database, email, FTP and others. A single physical machine is not only a single point of failure, but also has finite capacity for traffic, that in practice can be troublesome for a busy website or for a website that is experiencing transient bursts in traffic.
By clustering services across multiple hardware machines, and using load balancing you can eliminate single points of failure increasing availability of your website and other web services beyond that of ordinary single server hosting. A single server can require periodic reboots for software upgrades and the like, whereas in a clustered platform you can stagger the restarts such that the service is still available whilst still upgrading all necessary machines in the cluster.
Clustered hosting is similar to cloud hosting, in that the resources of many machines are available for a website to utilize on demand, making scalability a large advantage to a clustered hosting solution.