When 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). 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 ends
To enable a multiple-storage back ends, you must set the
enabled_backends 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,
The configuration group name is not related to the
After setting the
enabled_backendsflag on an existing cinder service, and restarting the Block Storage services, the original
hostservice is replaced with a new host service. The new service appears with a name like
$ cinder-manage volume update_host --currenthost CURRENTHOST --newhost CURRENTHOST@BACKEND
to convert current block devices to the new host name.
The options for a configuration group must be defined in the group (or
default options are used). All the standard Block Storage configuration
volume_driver, and so on) might be used in a
configuration group. Configuration values in the
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.LVMVolumeDriver volume_backend_name=LVM [lvmdriver-2] volume_group=cinder-volumes-2 volume_driver=cinder.volume.drivers.lvm.LVMVolumeDriver volume_backend_name=LVM [lvmdriver-3] volume_group=cinder-volumes-3 volume_driver=cinder.volume.drivers.lvm.LVMVolumeDriver volume_backend_name=LVM_b
In this configuration,
lvmdriver-2 have the same
volume_backend_name. If a volume creation requests the
LVM back end
name, the scheduler uses the capacity filter scheduler to choose the
most suitable driver, which is either
The capacity filter scheduler is enabled by default. The next section
provides more information. In addition, this example presents a
lvmdriver-3 back end.
For Fiber Channel drivers that support multipath, the configuration group requires the
use_multipath_for_image_xfer=trueoption. In the example below, you can see details for HPE 3PAR and EMC Fiber Channel drivers.
[3par] use_multipath_for_image_xfer = true volume_driver = cinder.volume.drivers.hpe.hpe_3par_fc.HPE3PARFCDriver volume_backend_name = 3parfc [emc] use_multipath_for_image_xfer = true volume_driver = cinder.volume.drivers.emc.emc_smis_fc.EMCSMISFCDriver volume_backend_name = emcfc
#Configure Block Storage scheduler multi back end
You must enable the filter_scheduler option to use multiple-storage back ends. The filter scheduler:
- Filters the available back ends. By default,
- Weights the previously filtered back ends. By default, the CapacityWeigher 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. For more information about filter and weighing, see filter_weigh_scheduler.
Before 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 lvm
Then, 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_iSCSI
This 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_b
This second volume type is named
lvm_gold and has
back end name.
To list the extra-specifications, use this command:
$ cinder --os-username admin --os-tenant-name admin extra-specs-list
If a volume type points to a
volume_backend_namethat does not exist in the Block Storage configuration, the
filter_schedulerreturns an error that it cannot find a valid host with the suitable back end.
When 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
cinder.conf described previously, the scheduler
creates this volume on
$ cinder create --volume_type lvm_gold --display_name test_multi_backend 1
This second volume is created on