Cloned from launchpad blueprint https://blueprints.launchpad.net/cinder/+spec/add-volume-usages-to-limits.

Description:

Cinder maintains current quota usages of each tenant in quota_usages db table. There is logic to calculate "gigabytes" used for both volumes and snapshots,
and the quotas api in cinder gives information of current usages for a particular tenant. 
But, this api is implemented as a cinder extension and there is a possibility that a service provider may not deploy this extension in their environment. In that case horizon will fail to show the usages, which was why horizon replaced quota apis with limit apis across all screens (in bug https://bugs.launchpad.net/horizon/+bug/1178694).

One way to tackle this problem is to enhance the limits API to include usage information in the response, as follows:

A)
 
{
    "limits": {
        "rate": [], 
        "absolute": {
            "maxTotalVolumeGigabytes": 1000,
            "maxTotalVolumes": 10,
            "totalGigabytes" : 50,
            "totalSnapshots": 6,
            "totalVolumes": 3
          }
    }
}

or 

B)
{
    "limits": {
        "rate": [],
        "absolute": {
            "maxTotalVolumeGigabytes": 1000,
            "maxTotalVolumes": 10
        },
        "usages" : {
            "totalGigabytes" : 50,
            "totalSnapshots": 6,
            "totalVolumes": 3
       } 
    }
}

option A) ensures consistency across openstack services while option B) seems ideal to separate out absolute and usage
figures.

Specification URL (additional information):

None