Adds spec for Hyper-V disk latency metrics

https://blueprints.launchpad.net/ceilometer/+spec/hyper-v-disk-latency-metrics

Change-Id: I9f4a78dd75b87e5e243e214d1c0958ff63fcc4b1

specs/kilo/hyper-v-disk-latency-metrics.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+=================================================================
+Adds disk latency metrics implementation in the Hyper-V Inspector
+=================================================================
+
+https://blueprints.launchpad.net/ceilometer/+spec/hyper-v-disk-latency-metrics
+
+High latency between I/O requests can be signs of issues. Collecting disk
+latency metrics can help us detect those issues. Hyper-V Inspector can collect
+those metrics.
+
+Problem description
+===================
+
+Disk latency metrics are important in telemetry and useful when determining
+instance's performance. This spec is about these stats and their implementation
+in the Hyper-V Inspector.
+
+Proposed change
+===============
+
+Add DiskLatencyPollster and PerDeviceDiskLatencyPollster pollsters, which
+create samples having the properties:
+* name: 'disk.latency'
+* type: 'gauge'
+* unit: 'ms'
+
+Add the method 'inspect_disk_latency' in Inspector and implementing it in the
+HyperVInspector, fetching disk latency stats data from Hyper-V VMs, located
+in the Msvm_AggregationMetricValue objects (further referred to as
+'metrics objects') associated with the VMs.
+The metrics objects 'MetricDefinitionId' must be the equal to the 'Id' of
+Msvm_AggregationMetricDefinition object having the Caption
+'Average Disk Latency'.
+
+Hyper-V disk metrics were introduced in Windows / Hyper-V Server 2012 R2
+(kernel version 6.3). They are not supported in the previous versions.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Pipeline impact
+---------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance/Scalability Impacts
+-------------------------------
+
+None
+
+Other deployer impact
+---------------------
+
+Users will have to add meter 'disk.latency' in the disk_source source in
+pipeline.yaml
+By default, the disk usage metrics collection is enabled in Nova, we just need
+to collect the data from the Hyper-V API.
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  <cbelu>
+
+Work Items
+----------
+
+* Adds the DiskLatencyPollster and PerDeviceDiskLatencyPollster pollsters
+* Adds the method 'inspector_disk_latency' in Inspector.
+* Implements the method 'inspect_disk_latency' in HyperVInspector.
+* Adds related unit tests.
+* Updates ceilometer measurements document.
+
+Future lifecycle
+================
+
+Once this feature is enabled, it needs tests and bug fixing in the next
+2 releases to avoid regression.
+
+Dependencies
+============
+
+* Windows / Hyper-V Server 2012 R2 (kernel version 6.3)
+* wmi 1.4.9+
+
+Testing
+=======
+
+Unit tests are needed to test the new pollsters and the implementation on
+the Hyper-V side.
+
+Documentation Impact
+====================
+
+The added metrics will need to be documented in the `measurements section`_.
+
+.. _measurements section: http://docs.openstack.org/developer/ceilometer/measurements.html
+
+References
+==========
+
+* [1] http://msdn.microsoft.com/en-us/library/cc768535%28v=bts.10%29.aspx