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Taikun OCP Guide

Table of Contents

Capabilities and Extra-Specs

Cloud Administrators create shared_file_systems_share_types with extra-specs
to:

  • influence the scheduler’s decision to place new shares, and
  • instruct the Shared File System service or its storage driver/s to
    perform certain special actions with respect to the users’ shares.

As an administrator, you can choose a descriptive name or provide
good descriptions for your share types to convey the share type
capabilities to end users. End users can view standard
tenant-visible extra-specs that can let them seek required
behavior and automate their applications accordingly. By design,
however, all other extra-specs of a share type are not exposed to
non-privileged users.

Types of Extra-Specs

The Shared File Systems service back-end storage drivers offer a wide
range of capabilities. The variation in these capabilities allows cloud
administrators to provide a storage service catalog to their end users.
Share type extra-specs tie-in with these capabilities.

Some back-end capabilities are very specific to a storage system, and
are opaque to the Shared File System service or the end users. These
capabilities are invoked with the help of “scoped” extra-specs. Using
scoped extra-specs is a way to provide programmatic directives to the
concerned storage driver to do something during share creation or share
manipulation. You can learn about the opaque capabilities through driver
documentation and configure these capabilities within share types as
scoped extra-specs (e.g.: hpe3par:nfs_options). The Shared File System
service scheduler ignores scoped extra-specs during its quest to find
the right back end to provision shares.

There are some back-end capabilities in manila that do matter to the
scheduler. For our understanding, lets call these non-scoped or
non-opaque capabilities. All non-scoped capabilities can be directly
used as share types extra-specs. They are considered by the scheduler’s
capabilities filter (and any custom filter defined by deployers).

You can get a list of non-scoped capabilities from the scheduler by
using:

$ manila pool-list --detail

The non-scoped capabilities can be of three types:

  • Capabilities pertaining to a specific back end storage
    system driver
    : For example, huawei_smartcache. No
    Shared File System service API relies on non-opaque back end specific
    capabilities.

  • Common capabilities that are not visible to end
    users
    : The manila community has standardized some
    cross-platform capabilities like thin_provisioning,
    dedupe, compression, qos,
    ipv6_support and ipv4_support. Values of these options
    do not matter to any Shared File System service APIs; however, they can
    signify something to the manila services themselves. For example when a
    back end supports thin_provisioning, the scheduler service performs
    over-provisioning, and if a back end does not report
    ipv6_support as True, the share-manager service drops IPv6
    access rules before invoking the storage driver to update access
    rules.

  • Common capabilities that are visible to end
    users
    : Some capabilities affect functionality exposed via the
    Shared File System service API. For example, not all back ends support
    snapshots, and even if they do, they may not support all of the snapshot
    operations. For example, cloning snapshots into new shares, reverting
    shares in-place to snapshots, etc.

    The support for these capabilities determines whether users would be
    able to perform certain control-plane operations with manila. For
    example, a back end driver may report snapshot_support=True
    allowing end users to create share snapshots, however, the driver can
    report create_share_from_snapshot_support=False. This reporting
    allows cloud administrators to create share types that support snapshots
    but not creating shares from snapshots. When a user uses such a share
    type, they will not be able to clone snapshots into new shares.
    Tenant-visible capabilities aid manila in validating requests and
    failing fast on requests it cannot accommodate. They also help level set
    the user expectations on some failures. For example, if snapshot_support
    is set to False on the share type, since users can see this, they will
    not invoke the create snapshot API, and even if they do, they will
    understand the HTTP 400 (and error message) in better context.

Important

All extra-specs are optional, except one:
driver_handles_share_servers.

Scheduler’s
treatment of non-scoped extra specs

The CapabilitiesFilter in the Shared File System scheduler 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. If “share_backend_name s!=
    cephfs” is used, any host not named “cephfs” can be chosen.

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

Common Capabilities

Common capabilities apply to multiple backends. Like all other
backend reported capabilities, these capabilities can be used verbatim
as extra_specs in share types used to create shares.

Share
type common capability extra-specs that are visible to end users:

  • driver_handles_share_servers is a special, required
    common capability. When set to True, the scheduler matches requests with
    back ends that can isolate user workloads with dedicated share servers
    exporting shares on user provided share networks.
  • 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.
  • mount_snapshot_support indicates that a driver is
    capable of exporting share snapshots for mounting. Users can provide and
    revoke access to mountable snapshots just like they can with their
    shares.
  • 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.
  • availability_zones indicates a comma separated list
    of availability zones that can be used for provisioning. Users can
    always provide a specific availability zone during share creation, and
    they will receive a synchronous failure message if they attempt to
    create a share in an availability zone that the share type does not
    permit. If you do not set this extra-spec, the share type is assumed to
    be serviceable in all availability zones known to the Shared File
    Systems service.

Share
type common capability extra-specs that are not visible to end
users:

  • 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. Drivers can
    support both dedupe and non-deduped shares in a single storage pool by
    reporting dedupe=[True, False]. You can make a share type
    use deduplication by setting this extra-spec to ‘<is> True’, or
    prevent it by setting this extra-spec to ‘<is> False’.

  • 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.
    Drivers can support compressed and non-compressed shares in a single
    storage pool by reporting compression=[True, False]. You
    can make a share type use compression by setting this extra-spec to
    ‘<is> True’, or prevent it by setting this extra-spec to
    ‘<is> False’.

  • thin_provisioning can be enabled where shares
    will not be guaranteed space allocations and overprovisioning will be
    enabled. This capability defaults to False. Back ends/pools that support
    thin provisioning 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. A driver can support thin
    provisioned and thick provisioned shares in the same pool by reporting
    thin_provisioning=[True, False].

    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.
    You 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.
  • 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.
  • provisioning:max_share_size can set the max size of
    share, the value must be an integer and greater than 0. If
    administrators set this capability as an extra-spec in a share type, the
    size of share created with the share type can not be greater than the
    specified value.
  • provisioning:min_share_size can set the min size of
    share, the value must be an integer and greater than 0. If
    administrators set this capability as an extra-spec in a share type, the
    size of share created with the share type can not be less than the
    specified value.

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