As you probably noticed, the majority of VPS hosting providers offer you a choice of tariff plans differing in technical characteristics, as well as virtualization technology. As for the latter parameter, in most cases we are talking about the two platforms – Xen and Open VZ. A user can clearly see that the Xen virtualization technology is usually 35-50% more expensive than OpenVZ. Why is that? Mostly, because of the resources distribution technology, and also because of some other differences that can explain the higher price.
The main feature which characterizes OpenVZ is using a single kernel for all VPS servers.
Disadvantages of using Open VZ:
- You can’t install an operational system other than the already installed Linux.
- The one and only file system serves all VPS. Therefore, if it fails, the failure will affect not only the owner of a certain VPS which failed, but also all other owners located on one physical server.
- You are not allowed to install an OS module you need yourself. You need to ask your hosting provider to do this.
- One kernel serves for dozens of VPS, which means that each newly ordered VPS brings additional strain on the server.
Peculiarities of Open VZ:
- Users can’t swap memory from the CPU.
- There are going to appear such errors as ‘Cannot allocate memory’ if more memory than guaranteed by the tariff plan has been used.
- Inconsistency between the declared and the real parameters of allocated memory. For instance, if it is declared that a VPS at Open VZ has 512 RAM, in reality the amount of RAM available is going to be around 470-480 Mb.
Advantages of Open VZ:
- High productivity of a VPS if there are few clients on one machine, i.e. there is no overselling.
- Change of a tariff plan and server parameters within a couple of seconds without rebooting the server.
- Low price.
What is in Open VZ for a web host?
- It doesn’t take long to set up necessary parameters.
- A chance to sell more resources than you really have. The thing is that a client doesn’t usually consume all the VPS parameters allocated to him. For instance, very often a client would only use 10 Gb out of 20 Gb available according to his tariff plan. Then the rest is going to be resold to new users (it is kind of similar to the ‘Pyramid’ principle). Some providers do not get too cheeky and only sell 2-3 times more resources than they really have at their disposal, while for others selling 10 times more resources doesn’t sound that bad.
Unlike Open VZ, Xen allows you to launch several dozen kernels on one server with insignificant productivity losses.
Advantages of Xen:
- You can install any operational system, including Windows. You can also make any changes to the system kernel without affecting the rest of VPS owners on the server.
- The file system of your VPS is independent and isn’t prone to failure in the situation when another server is experiencing problems.
- At any moment you are able to use available VPS resources to the fullest.
- Strict allocation of resources. For instance, if you have 256 Mb RAM when using the Xen virtualization platform, it means that all the 256 Mb are really available to you, unlike with Open VZ.
- A swap file is available.
- Isolation from other users on one physical server. Their bugs and errors aren’t going to affect you.
Disadvantages of Xen:
- Having to reboot your server every time you want to change the tariff plan parameters or the tariff plan itself.
- Higher price due to the absence of overselling server resources.
Those new to the VPS hosting are advised at first to buy a server at Open VZ, and together with it get acquainted with all the delights of the Linux system without having to overpay for the unused resources and the lost time.