Capabilities and Extra-Specs

Capabilities and Extra-Specs

Manila Administrators create share types with extra-specs to allow users to request a type of share to create. The Administrator chooses a name for the share type and decides how to communicate the significance of the different share types in terms that the users should understand or need to know. By design, most of the details of a share type (the extra- specs) are not exposed to users – only Administrators.

Share Types

Refer to the manila client command-line help for information on how to create a share type and set “extra-spec” key/value pairs for a share type.

Extra-Specs

There are 3 types of extra-specs: required, scoped, and un-scoped.

Manila requires the driver_handles_share_servers extra-spec.

Scoped extra-specs use a prefix followed by a colon to define a namespace for scoping the extra-spec. A prefix could be a vendor name or acronym and is a hint that this extra-spec key/value only applies to that vendor’s driver. Scoped extra-specs are not used by the scheduler to determine where a share is created (except for the special capabilities prefix). It is up to each driver implementation to determine how to use scoped extra-specs and to document them.

The prefix “capabilities” is a special prefix to indicate extra-specs that are treated like un-scoped extra-specs. In the CapabilitiesFilter the “capabilities:” is stripped from the key and then the extra-spec key and value are used as an un-scoped extra-spec.

Un-scoped extra-specs have a key that either starts with “capabilities:” or does not contain a colon. When the CapabilitiesFilter is enabled (it is enabled by default), the scheduler will only create a share on a backend that reports capabilities that match the share type’s un-scoped extra-spec keys.

The CapabilitiesFilter uses the following for matching operators:

  • No operator This defaults to doing a python ==. Additionally it will match boolean values.

  • <=, >=, ==, !=

    This does a float conversion and then uses the python operators as expected.

  • <in>

    This either chooses a host that has partially matching string in the capability or chooses a host if it matches any value in a list. For example, if “<in> sse4” is used, it will match a host that reports capability of “sse4_1” or “sse4_2”.

  • <or>

    This chooses a host that has one of the items specified. If the first word in the string is <or>, another <or> and value pair can be concatenated. Examples are “<or> 3”, “<or> 3 <or> 5”, and “<or> 1 <or> 3 <or> 7”. This is for string values only.

  • <is>

    This chooses a host that matches a boolean capability. An example extra-spec value would be “<is> True”.

  • =

    This does a float conversion and chooses a host that has equal to or greater than the resource specified. This operator behaves this way for historical reasons.

  • s==, s!=, s>=, s>, s<=, s<

    The “s” indicates it is a string comparison. These choose a host that satisfies the comparison of strings in capability and specification. For example, if “capabilities:replication_type s== dr”, a host that reports replication_type of “dr” will be chosen.

For vendor-specific capabilities (which need to be visible to the CapabilityFilter), it is recommended to use the vendor prefix followed by an underscore. This is not a strict requirement, but will provide a consistent look along-side the scoped extra-specs and will be a clear indicator of vendor capabilities vs. common capabilities.

Common Capabilities

For capabilities that apply to multiple backends a common capability can be created. Like all other backend reported capabilities, these capabilities can be used verbatim as extra_specs in share types used to create shares.

  • driver_handles_share_servers is a special, required, user-visible common capability. Added in Kilo.

  • dedupe - indicates that a backend/pool can provide shares using some deduplication technology. The default value of the dedupe capability (if a driver doesn’t report it) is False. In Liberty, drivers cannot report to the scheduler that they support both dedupe and non-deduped share. For each pool it’s either always on or always off, even if the drivers can technically support both dedupe and non-deduped in a pool. Since Mitaka, the logic is changed to allow a driver to report dedupe=[True, False] if it can support both dedupe and non-deduped in a pool. Administrators can make a share type use deduplication by setting this extra-spec to ‘<is> True’. Administrators can prevent a share type from using deduplication by setting this extra-spec to ‘<is> False’. Added in Liberty.

  • compression - indicates that a backend/pool can provide shares using some compression technology. The default value of the compression capability (if a driver doesn’t report it) is False. In Liberty, drivers cannot report to the scheduler that they support both compression and non-compression. For each pool it’s either always on or always off, even if the drivers can technically support both compression and non-compression in a pool. Since Mitaka, the logic is changed to allow a driver to report compression=[True, False] if it can support both compression and non-compression in a pool. Administrators can make a share type use compression by setting this extra-spec to ‘<is> True’. Administrators can prevent a share type from using compression by setting this extra-spec to ‘<is> False’. Added in Liberty.

  • thin_provisioning - shares will not be space guaranteed and overprovisioning will be enabled. This capability defaults to False. Backends/pools that support thin provisioning must report True for this capability. Administrators can make a share type use thin provisioned shares by setting this extra-spec to ‘<is> True’. If a driver reports thin_provisioning=False (the default) then it’s assumed that the driver is doing thick provisioning and overprovisioning is turned off. This was added in Liberty. In Liberty and Mitaka, the driver was required to configure one pool for thin and another pool for thick and report thin_provisioning as either True or False even if an array can technically support both thin and thick provisioning in a pool. In Newton, the logic is changed to allow a driver to report thin_provisioning=[True, False] if it can support both thin and thick provisioning in a pool. To provision a thick share on a back end that supports both thin and thick provisioning, set one of the following in extra specs:

{'thin_provisioning': 'False'}
{'thin_provisioning': '<is> False'}
{'capabilities:thin_provisioning': 'False'}
{'capabilities:thin_provisioning': '<is> False'}
  • qos - indicates that a backend/pool can provide shares using some QoS (Quality of Service) specification. The default value of the qos capability (if a driver doesn’t report it) is False. Administrators can make a share type use QoS by setting this extra-spec to ‘<is> True’ and also setting the relevant QoS-related extra specs for the drivers being used. Administrators can prevent a share type from using QoS by setting this extra-spec to ‘<is> False’. Different drivers have different ways of specifying QoS limits (or guarantees) and this extra spec merely allows the scheduler to filter by pools that either have or don’t have QoS support enabled. Added in Mitaka.

  • replication_type - indicates the style of replication supported for the backend/pool. This extra_spec will have a string value and could be one of writable, readable or dr. writable replication type involves synchronously replicated shares where all replicas are writable. Promotion is not supported and not needed. readable and dr replication types involve a single active or primary replica and one or more non-active or secondary replicas per share. In readable type of replication, non-active replicas have one or more export_locations and can thus be mounted and read while the active replica is the only one that can be written into. In dr style of replication, only the active replica can be mounted, read from and written into. Added in Mitaka.

  • snapshot_support - indicates whether snapshots are supported for shares created on the pool/backend. When administrators do not set this capability as an extra-spec in a share type, the scheduler can place new shares of that type in pools without regard for whether snapshots are supported, and those shares will not support snapshots.

  • create_share_from_snapshot_support - indicates whether a backend can create a new share from a snapshot. When administrators do not set this capability as an extra-spec in a share type, the scheduler can place new shares of that type in pools without regard for whether creating shares from snapshots is supported, and those shares will not support creating shares from snapshots.

  • revert_to_snapshot_support - indicates that a driver is capable of reverting a share in place to its most recent snapshot. When administrators do not set this capability as an extra-spec in a share type, the scheduler can place new shares of that type in pools without regard for whether reverting shares to snapshots is supported, and those shares will not support reverting shares to snapshots.

  • ipv4_support - indicates whether a back end can create a share that can be accessed via IPv4 protocol. If administrators do not set this capability as an extra-spec in a share type, the scheduler can place new shares of that type in pools without regard for whether IPv4 is supported.

  • ipv6_support - indicates whether a back end can create a share that can be accessed via IPv6 protocol. If administrators do not set this capability as an extra-spec in a share type, the scheduler can place new shares of that type in pools without regard for whether IPv6 is supported.

Reporting Capabilities

Drivers report capabilities as part of the updated stats (e.g. capacity) for their backend/pools. This is how a backend/pool advertizes its ability to provide a share that matches the capabilities requested in the share type extra-specs.

Developer impact

Developers should update their drivers to include all backend and pool capacities and capabilities in the share stats it reports to scheduler. Below is an example having multiple pools. “my” is used as an example vendor prefix:

{
    'driver_handles_share_servers': 'False',  #\
    'share_backend_name': 'My Backend',       # backend level
    'vendor_name': 'MY',                      # mandatory/fixed
    'driver_version': '1.0',                  # stats & capabilities
    'storage_protocol': 'NFS_CIFS',           #/
                                              #\
    'my_capability_1': 'custom_val',          # "my" optional vendor
    'my_capability_2': True,                  # stats & capabilities
                                              #/
    'pools': [
        {'pool_name':
           'thin-dedupe-compression pool',    #\
         'total_capacity_gb': 500,            #  mandatory stats for
         'free_capacity_gb': 230,             #  pools
         'reserved_percentage': 0,            #/
                                              #\
         'dedupe': True,                      # common capabilities
         'compression': True,                 #
         'snapshot_support': True,            #
         'create_share_from_snapshot_support': True,
         'revert_to_snapshot_support': True,
         'qos': True,                         # this backend supports QoS
         'thin_provisioning': True,           #
         'max_over_subscription_ratio': 10,   # (mandatory for thin)
         'provisioned_capacity_gb': 270,      # (mandatory for thin)
                                              #
                                              #
         'replication_type': 'dr',            # this backend supports
                                              # replication_type 'dr'
                                              #/
         'my_dying_disks': 100,               #\
         'my_super_hero_1': 'Hulk',           #  "my" optional vendor
         'my_super_hero_2': 'Spider-Man',     #  stats & capabilities
                                              #/
                                              #\
                                              # can replicate to other
         'replication_domain': 'asgard',      # backends in
                                              # replication_domain 'asgard'
                                              #/
         'ipv4_support': True,
         'ipv6_support': True,

        },
        {'pool_name': 'thick pool',
         'total_capacity_gb': 1024,
         'free_capacity_gb': 1024,
         'qos': False,
         'snapshot_support': True,
         'create_share_from_snapshot_support': False, # this pool does not
                                                      # allow creating
                                                      # shares from
                                                      # snapshots
         'revert_to_snapshot_support': True,
         'reserved_percentage': 0,
         'dedupe': False,
         'compression': False,
         'thin_provisioning': False,
         'replication_type': None,
         'my_dying_disks': 200,
         'my_super_hero_1': 'Batman',
         'my_super_hero_2': 'Robin',
         'ipv4_support': True,
         'ipv6_support': True,
        },
     ]
}

Work Flow

  1. Share Backends report how many pools and what those pools look like and are capable of to scheduler;

  2. When request comes in, scheduler picks a pool that fits the need best to serve the request, it passes the request to the backend where the target pool resides;

  3. Share driver gets the message and lets the target pool serve the request as scheduler instructed. Share type extra-specs (scoped and un-scoped) are available for the driver implementation to use as-needed.

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