Configure multiple-storage back endsWhen you configure multiple-storage back ends, you can
create several back-end storage solutions that serve the same
OpenStack Compute configuration and one cinder-volume
is launched for each back-end storage or back-end storage pool.In a multiple-storage back end configuration, each back end has a name
(volume_backend_name). Several back
ends can have the same name. In that case, the scheduler
properly decides which back end the volume has to be created
in.The name of the back end is declared as an
extra-specification of a volume type (such as,
volume_backend_name=LVM_iSCSI). When a
volume is created, the scheduler chooses an appropriate back
end to handle the request, according to the volume type
specified by the user.Enable multiple-storage back endsTo enable a multiple-storage back ends, you must set
the flag in the
cinder.conf file. This flag
defines the names (separated by a comma) of the
configuration groups for the different back ends: one name
is associated to one configuration group for a back end
(such as, [lvmdriver-1]).The configuration group name is not related to the
volume_backend_name.The options for a configuration group must be defined in
the group (or default options are used). All the standard
Block Storage configuration options
(volume_group,
volume_driver, and so on) might be
used in a configuration group. Configuration values in the
[DEFAULT] configuration group are
not used.These examples show three back ends:enabled_backends=lvmdriver-1,lvmdriver-2,lvmdriver-3
[lvmdriver-1]
volume_group=cinder-volumes-1
volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
volume_backend_name=LVM_iSCSI
[lvmdriver-2]
volume_group=cinder-volumes-2
volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
volume_backend_name=LVM_iSCSI
[lvmdriver-3]
volume_group=cinder-volumes-3
volume_driver=cinder.volume.drivers.lvm.LVMISCSIDriver
volume_backend_name=LVM_iSCSI_bIn this configuration, lvmdriver-1
and lvmdriver-2 have the same
volume_backend_name. If a volume
creation requests the LVM_iSCSI back
end name, the scheduler uses the capacity filter scheduler
to choose the most suitable driver, which is either
lvmdriver-1 or
lvmdriver-2. The capacity filter
scheduler is enabled by default. The next section provides
more information. In addition, this example presents a
lvmdriver-3 back end.Configure Block Storage scheduler multi back
endYou must enable the
option to use multiple-storage back ends. The filter scheduler:Filters the available back
ends. By default,
AvailabilityZoneFilter,
CapacityFilter and
CapabilitiesFilter are
enabled.Weights the previously
filtered back ends. By default, the
option is
enabled. When this option is enabled, the filter
scheduler assigns the highest weight to back ends
with the most available capacity.The scheduler uses filters and weights to pick the best
back end to handle the request. The scheduler uses volume
types to explicitly create volumes on specific back
ends.Volume typeBefore using it, a volume type has to be declared to
Block Storage. This can be done by the following
command:$cinder --os-username admin --os-tenant-name admin type-create lvmThen, an extra-specification has to be created to link
the volume type to a back end name. Run this
command:$cinder --os-username admin --os-tenant-name admin type-key lvm set volume_backend_name=LVM_iSCSIThis example creates a lvm volume
type with volume_backend_name=LVM_iSCSI
as extra-specifications.Create another volume type:$cinder --os-username admin --os-tenant-name admin type-create lvm_gold$cinder --os-username admin --os-tenant-name admin type-key lvm_gold set volume_backend_name=LVM_iSCSI_bThis second volume type is named
lvm_gold and has
LVM_iSCSI_b as back end
name.To list the extra-specifications, use this
command:$cinder --os-username admin --os-tenant-name admin extra-specs-listIf a volume type points to a
volume_backend_name that does
not exist in the Block Storage configuration, the
filter_scheduler returns an
error that it cannot find a valid host with the
suitable back end.UsageWhen you create a volume, you must specify the volume
type. The extra-specifications of the volume type are used
to determine which back end has to be used.
$cinder create --volume_type lvm --display_name test_multi_backend 1
Considering the cinder.conf described
previously, the scheduler creates this volume on
lvmdriver-1 or
lvmdriver-2.$cinder create --volume_type lvm_gold --display_name test_multi_backend 1This second volume is created on
lvmdriver-3.