[openstack-dev] [Nova] Nova compute reports the disk usage

Tuan Luong tuan.luong at ericsson.com
Wed Aug 3 15:13:28 UTC 2016

Hi Jay,
Thank you for the reply. Actually, I did ask this question to make sure that everything is still going well with disk usage report of Nova. We had the problem related to wrong report (IMHO it is wrong). The situation is below:

- We launch an instance with 600Gb of ephemeral disk of flavor without specifying extra ephemeral disk. The total free_disk before launching is 1025Gb, the total disk_available_least is 1016Gb.
- After successful launching, what we have is the value of disk_available_disk = -184Gb therefore we could not launch the next instance.

It seems like the value of disk_available_disk decreases 2*600Gb when I think it should be 600Gb. The value of free_disk after launching is calculated well. I would not believe that the disk_over_commit in this case is 600Gb. Otherwise, we also check the instance that indeed it has only 600Gb mounted as vdb.


-----Original Message-----
From: Jay Pipes [mailto:jaypipes at gmail.com] 
Sent: August 03, 2016 14:53
To: openstack-dev at lists.openstack.org
Subject: Re: [openstack-dev] [Nova] Nova compute reports the disk usage

On 08/03/2016 04:35 AM, Tuan Luong wrote:
> Hi,
> When we try to add ephemeral disk in booting instance, as we know that 
> it will create disk.local and the backing file in _/base. Both of them 
> are referred to the ephemeral disk. When nova reports the disk usage 
> of compute, does it count both of them for the used disk? What I see 
> in the resource/_tracker that it calculates the instance['ephemeral_gb'].

The resource tracker reports disk usage by adding up the root_gb + ephemeral_gb values of the *flavor* attribute of the instances assigned to that compute node.

Does that answer your question?


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