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I've had a few pretty idle VPS under OpenVZ, and while I generally don't reach the guaranteed RAM, it bothers me that my VPS "thinks" it has more RAM than it actually does. After all, exceeding the guaranteed RAM can result in killed processes, while on the other hand it is very natural for Linux to eat as much RAM as possible! (Given these competing forces, it is surprising hosting providers don't offer the no-burstable option widely.)

Given this scenario I'd rather not have that occasional burstable RAM, and instead have Linux "see" only the guaranteed RAM. I guess I could open a support ticket and see what happens, but I wonder if there's something I can do from this end.


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One thing to consider here is that OpenVZ provides what I call "fake VPSes", in that there is one single linux kernel that services the host and all of the VPSes. Contrast that with KVM, Xen, VMware ESXi, etc., where each VPS is completely separated from the others, including their kernel. As such, in OpenVZ, the disk caching you're talking about happens at the host level, not at the VPS level, so it's completely out of your control and not something you need to worry about. If you want this level of control, consider moving off of OpenVZ to a real VPS. – EEAA Aug 20 '12 at 13:43

Set the burst RAM value to the same as your guaranteed value, this leaves no room for burst and your VPS will only see the actual amount of RAM it has been promised.

OpenVZ only offers burst RAM if there is a gap between these values.

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Thanks, but... how do I set that burst RAM value? It is indeed higher in my case. Indeed, I'd say >95% of commercial providers offer X guranteed RAM, and 2X burst RAM. – sadpluto Aug 20 '12 at 13:01
You control that with the configuration parameters usually under /etc/vz/<veid>.conf – Frands Hansen Aug 20 '12 at 14:02

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