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

Tuan Luong tuan.luong at ericsson.com
Mon Aug 8 09:12:53 UTC 2016

Hi Chris,

We have tried to reproduce it in two blades that have the same configs. 
They are all empty of instance from very beginning. What we see that the 
scenario happens in one blade, another works as expect. Of course we use 
qcow image.

If i use the below calculation, it can explain the scenario but why it 
does not happen in the another blade that has the same config? Does it 
relate to the worst case you mention? (Since there is no instance 
running before reproducing then i could not find out what worst case 

- Free_disk = Total(file_system) - Total(actual disk used by instances) 
- _base directory

- Overcommit = Total(virtual size of instances) - Total(actual disk used 
by instances)

- Avai_disk_least = Free_disk - Overcommit



On 08/04/2016 05:03 PM, Tuan Luong wrote:
> Hi Chris,
> Actually, the system does not belong to us therefore we only had the log file. But it seems reasonable that besides the size of ephemeral diisk in _base, we also have the image of vm downloaded from Glance that consumes the disk capacity. That can make the strange value of disk_over_commit.
> I will check this situation later. Btw, thank you for your help.
> Tuan
> -----Original Message-----
> From: Chris Friesen [mailto:chris.friesen at windriver.com]
> Sent: August 04, 2016 15:57
> To: openstack-dev at lists.openstack.org
> Subject: Re: [openstack-dev] [Nova] Nova compute reports the disk usage
> On 08/04/2016 02:42 AM, Tuan Luong wrote:
>> Hi Chris,
>> Yes we used qcow image. However I still have something not clear. What I know is that:
>> - disk_available_least = free_disk - disk_over_commit
>> - disk_over_commit = int(virt_size) - physical_disk_size
>> Before launching:
>> - free_disk = 1025
>> - disk_available_least = 1016
>> If we use the normal flavor with 600Gb disk and no ephemeral., the result is good with both above value subtract 600Gb.
>> If we use the flavor without disk but 600Gb ephemeral, the result of disk_available_least = -184.
> Just a thought...did you clear out the _base directory between tests?  Or is there maybe an extra backing file sitting there consuming space?
> Chris
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