Open Stack

On Jan 6, 2015, at 12:56 AM, ppnaik <ppnaik at cse.iitb.ac.in> wrote:

> I have a multi node setup of openstack juno on centos 7. After I instantiate multiple VMs and check the nova-compute.log on compute nodes it shows a negative value for free disks even though the the physical system has a lot of free memory

This is pretty common, assuming you’re using a couple of defaults. If the VMs are backed by QCOW images, they’re sparsely allocated, which means that Openstack will assign it as much disk as the flavor is configured for, but not actually *use* it all. The compute node will track what’s been allocated, and can show negative numbers, even if the actual usage is low.

> 
> on the physical system. df -h
> 
> Filesystem               Size  Used Avail Use% Mounted on
> /dev/mapper/centos-root   50G  2.0G   49G   4% /
> devtmpfs                  16G     0   16G   0% /dev
> tmpfs                     16G     0   16G   0% /dev/shm
> tmpfs                     16G  281M   16G   2% /run
> tmpfs                     16G     0   16G   0% /sys/fs/cgroup
> /dev/mapper/centos-home  865G   33M  865G   1% /home
> /dev/sda1                494M  137M  358M  28% /boot

As for WHY you have the negative numbers, I don’t see a lot of use on any of your filesystems, but the default storage for VM disks is under /var/lib/nova/instances, so unless you’ve symlinked or changed the location, you’re actually using your root partition for VM storage.

> 
> nova-compute.log on compute node:
> 
> 2015-01-06 11:00:28.756 8123 AUDIT nova.compute.resource_tracker [-] Total physical ram (MB): 31911, total allocated virtual ram (MB): 17920
> 2015-01-06 11:00:28.756 8123 AUDIT nova.compute.resource_tracker [-] Free disk (GB): -113
> 2015-01-06 11:00:28.757 8123 AUDIT nova.compute.resource_tracker [-] Total usable vcpus: 16, total allocated vcpus: 10
> 
> What is the issue and how can I resolve it? Please help.
> 
> Thanks,
> 
> Priyanka

Cheers,
-j