Returns a list of vim.VsanHostDiskMapping objects representing disks
    in a ESXi host, filtered by their cannonical names.

    host_ref
        The vim.HostSystem object representing the host that contains the
        requested disks.

    cache_disk_ids
        The list of cannonical names of the cache disks to be retrieved. The
        canonical name of the cache disk is enough to identify the disk group
        because it is guaranteed to have one and only one cache disk.
        Default is None.

    get_all_disk_groups
        Specifies whether to retrieve all disks groups in the host.
        Default value is False.

def get_diskgroups(host_ref, cache_disk_ids=None, get_all_disk_groups=False):
    '''
    Returns a list of vim.VsanHostDiskMapping objects representing disks
    in a ESXi host, filtered by their cannonical names.

    host_ref
        The vim.HostSystem object representing the host that contains the
        requested disks.

    cache_disk_ids
        The list of cannonical names of the cache disks to be retrieved. The
        canonical name of the cache disk is enough to identify the disk group
        because it is guaranteed to have one and only one cache disk.
        Default is None.

    get_all_disk_groups
        Specifies whether to retrieve all disks groups in the host.
        Default value is False.
    '''
    hostname = get_managed_object_name(host_ref)
    if get_all_disk_groups:
        log.trace('Retrieving all disk groups on host \'%s\'', hostname)
    else:
        log.trace('Retrieving disk groups from host \'%s\', with cache disk '
                  'ids : (%s)', hostname, cache_disk_ids)
        if not cache_disk_ids:
            return []
    try:
        vsan_host_config = host_ref.config.vsanHostConfig
    except vim.fault.NoPermission as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareApiError(
            'Not enough permissions. Required privilege: '
            '{0}'.format(exc.privilegeId))
    except vim.fault.VimFault as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareApiError(exc.msg)
    except vmodl.RuntimeFault as exc:
        log.exception(exc)
        raise salt.exceptions.VMwareRuntimeError(exc.msg)
    if not vsan_host_config:
        raise salt.exceptions.VMwareObjectRetrievalError(
            'No host config found on host \'{0}\''.format(hostname))
    vsan_storage_info = vsan_host_config.storageInfo
    if not vsan_storage_info:
        raise salt.exceptions.VMwareObjectRetrievalError(
            'No vsan storage info found on host \'{0}\''.format(hostname))
    vsan_disk_mappings = vsan_storage_info.diskMapping
    if not vsan_disk_mappings:
        return []
    disk_groups = [dm for dm in vsan_disk_mappings if
                   (get_all_disk_groups or
                    (dm.ssd.canonicalName in cache_disk_ids))]
    log.trace(
        'Retrieved disk groups on host \'%s\', with cache disk ids : %s',
        hostname, [d.ssd.canonicalName for d in disk_groups]
    )
    return disk_groups