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Linux Virtual Private Servers (VPS) act like Full Dedicated Servers and are completely independent from other VPS’s hosted on the same machine. Like standard dedicated server ental Your VPS is its own secure, environment running its own operating system version and software and libraries and ports. A VPS differs from a reseller account as you have “root” or administrator access and therefore full control over services offered, software and libraries.
The additonal overhead of running a Xen Virtual Dedicated Server is typically very low. This makes it potentially more efficient than the excellent User Mode Linux (UML) which has proven itself well in the virtual hosting field. UML uses emulated system calls and disk drivers which make it slower, when it comes to context switches and disk I/O. Xen is a “hypervisor” with the host operating system a Virtual Machine (VM) under it. This makes for a very low overhead of typically 2-8%.
Linux VServer is similar to the popular but proprietory Virtuozzo kernel from SW-Soft. Both VServer and Virtuozzo are basically a shared kernel with security isolation (a chrooted init) using context and capabilities to limit the power of the superuser within the VM. So they lack many of the features of a true virtual machine, such as no low level networking, and the ability to use certain kernel modules. Xen allows you to maintain the virtual machine as if it were a real hardware device, using the common and well known up dating tools such as apt-get and yum, without having to create specialist template files.
One advantages to a Hosting ISP of Virtuozzo might be that the file system is entirely quota based which allows for a slight “overselling” of web space, similar to normal “virtual hosting.” However with Virtuozzo there are some hardware limitations, as the Virtuozzo kernel does not support the range of hardware as the “standard” Linux kernel, though SW-Soft have been prepared to produce special versions for large customers, for example support for AMD processors or specific RAID devices
We are asked if a Virtual Machine with just 32MB or 64MB of RAM is actually useful for anything, but with Linux the memory is used efficiently so for testing software under different operating systems, hosting a few mainly static websites, or for use as a root shell account on a well performing network (for perhaps training purposes) they are ideal.
We have put Xen Virtual Dedicated Servers to use in the following applications:
- Web Server
- Mail Server
- DNS Server
- Mail or DNS secondary
- Development Box
- An RPM build environment
- Nagios Network Monitoring Node
- Shell Account Hosting
- An advanced reseller solution (with Control Panel)
Inside the virtual machine the “experience” is very similar to a real hardware server. You have “root” level access to a command shell and therefore complete control over system processes, such as web or mail server software or databases. Indeed you can install your own versions of software and libraries. Just like a real hardware dedicated server it is neccessary to keep your VPS updated with latest security patches and bug fixes from the operating system vendor. A Xen VPS can be maintained using the established backup tools, such as “up2date” “yum” and “apt-get.” You can can also use “rpm” within the VPS and compile software from source.
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