OpenStack Block Storage enables you to choose a volume back end
according to free_capacity and
allocated_capacity. The volume number weigher feature lets
the scheduler choose a volume back end based on its volume number in the
volume back end. This can provide another means to improve the volume
back ends’ I/O balance and the volumes’ I/O performance.

Enable volume number weigher

To enable a volume number weigher, set the
scheduler_default_weighers to
VolumeNumberWeigher flag in the cinder.conf
file to define VolumeNumberWeigher as the selected
weigher.

Configure multiple-storage
back ends

To configure VolumeNumberWeigher, use
LVMVolumeDriver as the volume driver.

This configuration defines two LVM volume groups:
stack-volumes with 10 GB capacity and
stack-volumes-1 with 60 GB capacity. This example
configuration defines two back ends:

scheduler_default_weighers=VolumeNumberWeigher
enabled_backends=lvmdriver-1,lvmdriver-2
[lvmdriver-1]
volume_group=stack-volumes
volume_driver=cinder.volume.drivers.lvm.LVMVolumeDriver
volume_backend_name=LVM

[lvmdriver-2]
volume_group=stack-volumes-1
volume_driver=cinder.volume.drivers.lvm.LVMVolumeDriver
volume_backend_name=LVM

Volume type

Define a volume type in Block Storage:

$ openstack volume type create lvm

Create an extra specification that links the volume type to a
back-end name:

$ openstack volume type set lvm --property volume_backend_name=LVM

This example creates a lvm volume type with
volume_backend_name=LVM as extra specifications.

Usage

To create six 1-GB volumes, run the openstack volume create --size 1 --type lvm volume1
command six times:

$ openstack volume create --size 1 --type lvm volume1

This command creates three volumes in stack-volumes and
three volumes in stack-volumes-1.

List the available volumes:

# lvs
LV                                          VG              Attr      LSize  Pool Origin Data%  Move Log Copy%  Convert
volume-3814f055-5294-4796-b5e6-1b7816806e5d stack-volumes   -wi-a----  1.00g
volume-72cf5e79-99d2-4d23-b84e-1c35d3a293be stack-volumes   -wi-a----  1.00g
volume-96832554-0273-4e9d-902b-ad421dfb39d1 stack-volumes   -wi-a----  1.00g
volume-169386ef-3d3e-4a90-8439-58ceb46889d9 stack-volumes-1 -wi-a----  1.00g
volume-460b0bbb-d8a0-4bc3-9882-a129a5fe8652 stack-volumes-1 -wi-a----  1.00g
volume-9a08413b-0dbc-47c9-afb8-41032ab05a41 stack-volumes-1 -wi-a----  1.00g