This Ruby example attaches an existing NFS storage domain, mydata, to an existing data center, mydc. This example is used to attach both data and ISO storage domains.

# Get the reference to the root of the services tree:
system_service = connection.system_service

# Locate the service that manages the storage domains and use it to
# search for the storage domain:
sds_service = system_service.storage_domains_service
sd = sds_service.list(search: 'name=mydata')[0]

# Locate the service that manages the data centers and use it to
# search for the data center:
dcs_service = system_service.data_centers_service
dc = dcs_service.list(search: 'name=mydc')[0]

# Locate the service that manages the data center where you want to
# attach the storage domain:
dc_service = dcs_service.data_center_service(dc.id)

# Locate the service that manages the storage domains that are attached
# to the data centers:
attached_sds_service = dc_service.storage_domains_service

# Use the "add" method of service that manages the attached storage
# domains to attach it:
attached_sds_service.add(
  OvirtSDK4::StorageDomain.new(
    id: sd.id
  )
)

# Wait until the storage domain is active:
attached_sd_service = attached_sds_service.storage_domain_service(sd.id)
loop do
  sleep(5)
  sd = attached_sd_service.get
  break if sd.status == OvirtSDK4::StorageDomainStatus::ACTIVE
end

For more information, see http://www.rubydoc.info/gems/ovirt-engine-sdk/OvirtSDK4/StorageDomainsService:add.