.. _driver_filter_goodness_weigher: ========================================================== Configure and use driver filter and weighing for scheduler ========================================================== OpenStack manila enables you to choose a share back end based on back-end specific properties by using the DriverFilter and GoodnessWeigher for the scheduler. The driver filter and weigher scheduling can help ensure that the scheduler chooses the best back end based on requested share properties as well as various back-end specific properties. What is driver filter and weigher and when to use it ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The driver filter and weigher give you the ability to more finely control how manila scheduler chooses the best back end to use when handling a share provisioning request. One example scenario where using the driver filter and weigher can be if a back end that utilizes thin-provisioning is used. The default filters use the ``free capacity`` property to determine the best back end, but that is not always perfect. If a back end has the ability to provide a more accurate back-end specific value, it can be used as part of the weighing process to find the best possible host for a new share. Some more examples of the use of these filters could be with respect to back end specific limitations. For example, some back ends may be limited by the number of shares that can be created on them, or by the minimum or maximum size allowed per share or by the fact that provisioning beyond a particular capacity affects their performance. The driver filter and weigher can provide a way for these limits to be accounted for during scheduling. Defining your own filter and goodness functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can define your own filter and goodness functions through the use of various capabilities that manila exposes. Capabilities exposed include information about the share request being made, ``share_type`` settings, and back-end specific information about drivers. All of these allow for a lot of control over how the ideal back end for a share request will be decided. The ``filter_function`` option is a string defining a function that will determine whether a back end should be considered as a potential candidate by the scheduler. The ``goodness_function`` option is a string defining a function that will rate the quality of the potential host (0 to 100, 0 lowest, 100 highest). .. important:: The driver filter and weigher will use default values for filter and goodness functions for each back end if you do not define them yourself. If complete control is desired then a filter and goodness function should be defined for each of the back ends in the ``manila.conf`` file. Supported operations in filter and goodness functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Below is a table of all the operations currently usable in custom filter and goodness functions created by you: +--------------------------------+-------------------------+ | Operations | Type | +================================+=========================+ | +, -, \*, /, ^ | standard math | +--------------------------------+-------------------------+ | not, and, or, &, \|, ! | logic | +--------------------------------+-------------------------+ | >, >=, <, <=, ==, <>, != | equality | +--------------------------------+-------------------------+ | +, - | sign | +--------------------------------+-------------------------+ | x ? a : b | ternary | +--------------------------------+-------------------------+ | abs(x), max(x, y), min(x, y) | math helper functions | +--------------------------------+-------------------------+ .. caution:: Syntax errors in filter or goodness strings are thrown at a share creation time. Available capabilities when creating custom functions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are various properties that can be used in either the ``filter_function`` or the ``goodness_function`` strings. The properties allow access to share info, qos settings, extra specs, and so on. The following capabilities are currently available for use: Host capabilities for a back end -------------------------------- host The host's name share\_backend\_name The share back end name vendor\_name The vendor name driver\_version The driver version storage\_protocol The storage protocol qos Boolean signifying whether QoS is supported total\_capacity\_gb The total capacity in gibibytes allocated\_capacity\_gb The allocated capacity in gibibytes free\_capacity\_gb The free capacity in gibibytes reserved\_percentage The reserved storage percentage driver\_handles\_share\_server The driver mode used by this host thin\_provisioning Whether or not thin provisioning is supported by this host updated Last time this host's stats were updated consistency\_group\_support Whether or not the back end supports creation of consistency groups dedupe Whether or not dedupe is supported by this host compression Whether or not compression is supported by this host snapshot\_support Whether or not snapshots are supported by this host replication\_domain The replication domain of this host replication\_type The replication type supported by this host provisioned\_capacity\_gb The provisioned capacity of this host in gibibytes pools This host's storage pools max\_over\_subscription\_ratio This hosts's over subscription ratio for thin provisioning Capabilities specific to a back end ----------------------------------- These capabilities are determined by the specific back end you are creating filter and goodness functions for. Some back ends may not have any capabilities available here. Requested share capabilities ---------------------------- availability\_zone\_id ID of the availability zone of this share share\_network\_id ID of the share network used by this share share\_server\_id ID of the share server of this share host Host name of this share is\_public Whether or not this share is public snapshot\_support Whether or not snapshots are supported by this share status Status for the requested share share\_type\_id The share type ID share\_id The share ID user\_id The share's user ID project\_id The share's project ID id The share instance ID replica\_state The share's replication state replication\_type The replication type supported by this share snapshot\_id The ID of the snapshot of which this share was created from size The size of the share in gibibytes share\_proto The protocol of this share source\_cgsnapshot\_member\_id The ID of the consistency group snapshot member consistency\_group\_id This share consistency group ID metadata General share metadata The most used capability from this list will most likely be the ``size``. Extra specs for the requested share type ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ View the available properties for share types by running: .. code-block:: console $ manila extra-specs-list Driver filter and weigher usage examples ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Below are examples for using the filter and weigher separately, together, and using driver-specific properties. Example ``manila.conf`` file configuration for customizing the filter function: .. code-block:: ini [default] enabled_backends = generic1, generic2 [generic1] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC1 filter_function = "share.size < 10" [generic2] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC2 filter_function = "share.size >= 10" The above example will filter share to different back ends depending on the size of the requested share. Shares with a size less than 10 GB are sent to generic1 and shares with a size greater than or equal to 10 GB are sent to generic2. Example ``manila.conf`` file configuration for customizing the goodness function: .. code-block:: ini [default] enabled_backends = generic1, generic2 [generic1] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC1 goodness_function = "(share.size < 5) ? 100 : 50" [generic2] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC2 goodness_function = "(share.size >= 5) ? 100 : 25" The above example will determine the goodness rating of a back end based on the requested share's size. The example shows how the ternary if statement can be used in a filter or goodness function. If a requested share is of size 10 GB then generic1 is rated as 50 and generic2 is rated as 100. In this case generic2 wins. If a requested share is of size 3 GB then generic1 is rated 100 and generic2 is rated 25. In this case generic1 would win. Example ``manila.conf`` file configuration for customizing both the filter and goodness functions: .. code-block:: ini [default] enabled_backends = generic1, generic2 [generic1] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC1 filter_function = "stats.total_capacity_gb < 500" goodness_function = "(share.size < 25) ? 100 : 50" [generic2] share_driver = manila.share.drivers.generic.GenericShareDriver share_backend_name = GENERIC2 filter_function = "stats.total_capacity_gb >= 500" goodness_function = "(share.size >= 25) ? 100 : 75" The above example combines the techniques from the first two examples. The best back end is now decided based on the total capacity of the back end and the requested share's size. Example ``manila.conf`` file configuration for accessing driver specific properties: .. code-block:: ini [default] enabled_backends = example1, example2, example3 [example1] share_driver = manila.share.drivers.example.ExampleShareDriver share_backend_name = EXAMPLE1 filter_function = "share.size < 5" goodness_function = "(capabilities.provisioned_capacity_gb < 30) ? 100 : 50" [example2] share_driver = manila.share.drivers.example.ExampleShareDriver share_backend_name = EXAMPLE2 filter_function = "shares.size < 5" goodness_function = "(capabilities.provisioned_capacity_gb < 80) ? 100 : 50" [example3] share_driver = manila.share.drivers.example.ExampleShareDriver share_backend_name = EXAMPLE3 goodness_function = "55" The above is an example of how back-end specific capabilities can be used in the filter and goodness functions. In this example, the driver has a ``provisioned_capacity_gb`` capability that is being used to determine which back end gets used during a share request. In the above example, ``example1`` and ``example2`` will handle share requests for all shares with a size less than 5 GB. ``example1`` will have priority until the provisioned capacity of all shares on it hits 30 GB. After that, ``example2`` will have priority until the provisioned capacity of all shares on it hits 80 GB. ``example3`` will collect all shares greater or equal to 5 GB as well as all shares once ``example1`` and ``example2`` lose priority.