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.
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.