Configure and use driver filter and weighing for scheduler

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
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
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:

$ 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.

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