Bug 1639903

Description of problem:
Currently when Manila reports data into the telemetry services they are represented in Gnocchi by the archive policy called "low" which does an average of the current value compared to the previous values instead of showing the size of the share in question. We will need to either modify the default archive policy to include "last" as one of the aggregation methods or create a new archive policy and enable "last" as one of the aggregation methods.

Version-Release number of selected component (if applicable):
N/A


How reproducible:
100%

Steps to Reproduce:
manila create --name metrics-test NFS 1
manila extend metrics-test 5
manila shrink metrics-test 2
manila shrink metrics-test 1
manila extend metrics-test 10
manila shrink metrics-test 5

openstack metric measures show 1e97387e-5bf4-4332-8198-dbee481f8a60
+---------------------------+-------------+-------+
| timestamp                 | granularity | value |
+---------------------------+-------------+-------+
| 2018-10-09T09:10:00-04:00 |       300.0 |   1.0 |
| 2018-10-09T09:25:00-04:00 |       300.0 |   3.0 |
| 2018-10-09T09:35:00-04:00 |       300.0 |   3.5 |
| 2018-10-10T16:55:00-04:00 |       300.0 |   1.5 |
| 2018-10-10T17:55:00-04:00 |       300.0 |  5.25 |
| 2018-10-12T17:10:00-04:00 |       300.0 |   7.5 |
+---------------------------+-------------+-------+


Actual results:
The metrics that Manila reports are not presented accurately due to not having the correct aggregation method applied to an archive policy (either the default or a new one).

Expected results:
Manila's share size metrics shall be reported correctly by Gnocchi by specifying a correct aggregation method.


Additional info:
The metrics that Manila is reporting are correct, but are merely being displayed incorrectly. Fixing this should be as simple as documenting how to create an appropriate archive policy in Gnocchi or how to modify the existing default archive policy to display the information correctly.