[Openstack-operators] over commit ratios
subbu at subbu.org
Wed Apr 22 15:44:07 UTC 2015
In addition to these factors, collocation happens to be another key source of noise. By collocation I mean VMs doing the same/similar work running on the same hypervisor. This happens under low capacity situations when the scheduler could not enforce anti-affinity.
> On Apr 22, 2015, at 5:09 AM, George Shuklin <george.shuklin at gmail.com> wrote:
> Yes, it really depends on the used backing technique. We using SSDs and raw images, so IO is not an issue.
> But memory is more important: if you lack IO capability you left with slow guests. If you lack memory you left with dead guests (hello, OOM killer).
> BTW: Swap is needed not to swapin/swapout, but to relief memory pressure. With properly configured memory swin/swout should be less than 2-3.
> On 04/22/2015 09:49 AM, Tim Bell wrote:
>> I'd also keep an eye on local I/O... we've found this to be the resource which can cause the worst noisy neighbours. Swapping makes this worse.
>>> -----Original Message-----
>>> From: George Shuklin [mailto:george.shuklin at gmail.com]
>>> Sent: 21 April 2015 23:55
>>> To: openstack-operators at lists.openstack.org
>>> Subject: Re: [Openstack-operators] over commit ratios
>>> It's very depend on production type.
>>> If you can control guests and predict their memory consumption, use it as base
>>> for ratio.
>>> If you can't (typical for public clouds) - use 1 or smaller with
>>> reserved_host_memory_mb in nova.conf.
>>> And one more: some swap sapce is really necessary. Add at least twice of
>>> reserved_host_memory_mb - it really improves performance and prevents
>>> strange OOMs in the situation of very large host with very small dom0 footprint.
>>> On 04/21/2015 10:59 PM, Caius Howcroft wrote:
>>>> Just a general question: what kind of over commit ratios do people
>>>> normally run in production with?
>>>> We currently run 2 for cpu and 1 for memory (with some held back for
>>>> default['bcpc']['nova']['ram_allocation_ratio'] = 1.0
>>>> default['bcpc']['nova']['reserved_host_memory_mb'] = 1024 # often
>>>> larger default['bcpc']['nova']['cpu_allocation_ratio'] = 2.0
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