Configure and use driver filter and weighing for scheduler¶

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).

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:

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:

Extra specs for the requested share type¶

View the available properties for share types by running:

$ 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:

[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:

[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:

[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:

[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.