How well are resources governed in VPSes?

raindog308

The recent thread about a customer who generated a load of 65 made me wonder how well resources are governed in a VPS. I'm thinking of common technologies like OvZ, Xen, KVM.

For disk - I don't think there's anything to guarantee or cap I/O, is there?

For memory - it's either there or it's not, right? You can oversell but ultimately if you give a VPS 512MB, that's all it can use (leaving out burst memory, swap, etc.)

So that leaves CPU. If you have an 8-core box and you give a VPS 1 core, they can max out a core's worth, but that's the limit of what they can do, right? So in theory I could be running 1 core at 100% but the other would be sitting there idle or in use by other VPSes?

Just wondering how tall the inter-VPS walls are.

BlackoutIsHere

I was wondering as well. Anyone care to share?

yomero

@raindog308 said: For disk - I don't think there's anything to guarantee or cap I/O, is there?

In KVM yes, in OpenVZ there is an ioprio option

@raindog308 said: For memory

Well, we already know lol

@raindog308 said: So that leaves CPU

Hmmm, most providers give that "fair share" based in a "cpuunits" param, I guess everybody gets "1000", so is fair.
Some providers have set "cpulimit" to give a fixed percentage of CPU. That's OpenVZ

For KVM, afaik the cpu scheduling just sucks.

For xen apparently you have fine control too

Shigawire

Isn't it also possible to limit your container to a certain percentage of a core?

Edit: too late ;(

craigb

Linux cgroups are used by savvy providers to partition host resources to client KVMs (example: OpenITC): https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

fileMEDIA

It´s possible to limit cpu in kvm too, but not implemented in solusvm (only in beta). http://libvirt.org/formatdomain.html#elementsCPUAllocation

Microlinux

You can use cgroups with RHEL6-based VZ kernels.

yomero

@Microlinux said: You can use cgroups with RHEL6-based VZ kernels.

@craigb said: OpenITC

They do that?

Very interesting information BTW, bookmarked

serverian

@craigb said: Linux cgroups are used by savvy providers to partition host resources to client KVMs (example: OpenITC): https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt

I thought KVM is already using cgroups to allocate and cap things.