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OpenVZ or Xen ?

January 30th, 2009
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OpenVZ:
Advantages: allows overselling. Very light weight. Can accommodate more Virtual Machines in a server.

Disadvantage: There is no per vps swap.

Why this is important:

OpenVZ will KILL your application if it goes beyond the limit, and this can cause some trouble. There are people out there who want to host oracle on a 64MB vps, and with such customers, using openVZ will lead to constant application crashes, which ultimately will be blamed on the provider. (This is actually something that is common with openvz/virtuozzo hosting in general; you can check some threads at wht).

With Xen, each vps has its own swap, and thus you get an EXACT dedicated server like environment, but with lesser resources. So here, the customers applications will NOT crash, but rather it will become slower. Also, majority of the applications, like apache, spamassassin expects a lot of memory, and openVZ makes memory a very valuable commodity.

So generally my recommendation is that: For friendly customers use openVZ, and use a lot of burst memory. For not-so-friendly customers, use Xen. And that is why we are providing transparent migration. You can start a customer on openVZ, and see how it works out, and if he is getting too many application crashes, you can move him to the SAME configuration on Xen, and he should be able to do fine, though his application would be slower.

Tags: Apache, burst, Memory, OpenVZ, oracle, swap, Virtuozzo, Virtuozzo, xen

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Virtual Server : Guaranteed Memory and Burstable Memory

January 30th, 2009
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Guaranteed memory is defined as the usable memory out of the memory available in VPS. This is available for the user at all time. Very often this guaranteed memory can be changed to burstable memory by the VPS.

Burstable memory set a maximum limit for the memory available where as guaranteed memory is a minimum limit. That is, even if the guaranteed memory is exhausted, the users of VPS can use the memory up to the limit of burstable memory. The simplest example to understand the difference is: if the guaranteed memory of a VPS is 256mb and the burstable memory limit is 1024 mb, the users can use the remaining 768MB RAM once their guaranteed memory is completely used up. This is possible only if the host server has that much memory available with it.

It is always a procedure to keep certain part of the memory in host server as burstable. This can be used by the virtual servers when they are in need of extra memory. Also the guaranteed memory unused in any virtual server can be used by other virtual servers when they want burstable memory. It is known that guaranteed memory should be available for use for the virtual servers. So when they are in need of guaranteed RAM, they usually kill the processes that use their memory as burstable to get the memory released. So it is always better not to use the burstable memory unless it is so needed.

When trying to get a VPS server, it should be clearly understood that the memory availability that they demand is not burst memory. The guaranteed memory must be available in sufficient amount to get proper working in VPS. The memory burstable is not readily available always as it can be obtained only on a lapse of guaranteed memory by other virtual servers in the system.

Tags: Burstable, Guarante, Memory, Virtual Server, Virtuozzo

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