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VCPU used > VCPU total [closed]

asked 2014-03-13 10:20:06 -0500

bo-zhang gravatar image

Hello everyone,

I meet two interesting problems.

the first one is: When I run devstack-havanna in my server, in the dashboard, it show that VCPUs(total) = 4. But I could launch 20 instances (admin:10 and demo:10), so in the dashboard, it show VCPUs(used) = 20. It's really strange, because when I run the devstack, there is no failure!! (My server has 4 processors, and cpu cores is 4, model name is Intel(R) Xeon(R))

the second one is: If we want to launch an instance in flavor m1.small (RAM: 2G, DISK:20G), the status of instance always fall into Error. but my server has 15G RAM and 215G DISK. The fault message from "nova show ......." is "no valid host could be found."

I think it's not normal and hope same one could help me. Thanks in advance

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Closed for the following reason the question is answered, right answer was accepted by mpetason
close date 2014-06-09 11:23:47.102353


can you share the logs from the file /var/log/nova/nova-compute.log and provide some brief idea on your setup, like hypervisor,topology....etc

prabhakar gravatar imageprabhakar ( 2014-03-13 10:40:58 -0500 )edit

Excuse me, I don't have this file. In fact in /var/log, there in no nova directory. In /opt/stack/log, there is just the log for execution of Devstack.

bo-zhang gravatar imagebo-zhang ( 2014-03-13 11:41:11 -0500 )edit

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answered 2014-03-13 10:46:17 -0500

mpetason gravatar image

It has to do with oversubscription in the nova configuration. I think the default is 1.5X for memory and then 16x for CPUs. You just aren't supposed to give an instance more vcpus than total physical(hypethreaded = physical x 2) cpus.

If you get on the compute node and look at:


You should be able to see how many resources you have left. If you don't have enough space/cpu/memory then it will fail when you launch an instance over the current resources.

It also matters where nova is storing the instances, if it's /var/lib/nova/volumes and that's not mounted to the disk that has 215G free then you won't have enough space for the disks behind the instances.

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Asked: 2014-03-13 10:20:06 -0500

Seen: 3,480 times

Last updated: Mar 13 '14