[Openstack-operators] over commit ratios

George Shuklin george.shuklin at gmail.com
Tue Apr 21 21:55:10 UTC 2015

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 

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 OS/ceph)
> i.e.:
> 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
> Caius

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