Incorrect available space being reported by cinder scheduler

Issue

• I have successfully deployed a Highly Available (HA) OpenStack cloud using the RHEL OSP Installer (rhel-osp-installer-0.5.5-5.el7ost.noarch). Our cloud configuration consists of three controller nodes and two compute nodes. I am using the default Neutron Networking, RabbitMQ, RHEL OSP6 on RHEL7 deployment option.

• Cinder is configured to use the NetApp driver backend with NFS. Storage Family selected is Clustered Data ONTAP.

Controller node:
[root@os3ctrl02 ~]# df -h
Filesystem                                  Size  Used Avail Use% Mounted on
/dev/mapper/vg_root-lv_root                  14G  5.0G  8.6G  37% /
devtmpfs                                    1.9G     0  1.9G   0% /dev
tmpfs                                       1.9G  245M  1.7G  13% /dev/shm
tmpfs                                       1.9G  185M  1.7G  10% /run
tmpfs                                       1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/vda2                                   477M  124M  329M  28% /boot
tmpfs                                       1.9G  185M  1.7G  10% /run/netns
xx.xx.xx.xx:/nfs_openstack_glance_dev_vol01   95G  411M   95G   1% /var/lib/glance/images
xx.xx.xx.xx:/nfs_openstack_cinder_dev_vol01   95G   28G   68G  29% /var/lib/cinder/mnt/dc4223e54675eae6c88e9e9a5975db40

• Note the cinder NFS share 'xx.xx.xx.xx:/nfs_openstack_cinder_dev_vol01' is reporting 68 GB available. I am launching an instance and it fails to launch with the following message in /var/log/cinder/scheduler.log:

2015-04-17 15:33:07.575 32331 WARNING cinder.scheduler.filters.capacity_filter [req-212b9fe5-9f4b-4969-aad3-16ad3eca78a7 8612ed5d8c794e9499bc2b6152bec6ad cc3dbcabf1d04bbd875f22f824dd0d5f - - -] Insufficient free space for volume creation on host ha-controller#10.8.1.201:/nfs_openstack_cinder_dev_vol01 (requested / avail): 20/18.0
2015-04-17 15:33:07.579 32331 WARNING cinder.scheduler.filter_scheduler [req-212b9fe5-9f4b-4969-aad3-16ad3eca78a7 8612ed5d8c794e9499bc2b6152bec6ad cc3dbcabf1d04bbd875f22f824dd0d5f - - -] No weighed hosts found for volume with properties: {}
2015-04-17 15:33:07.619 32331 ERROR cinder.scheduler.flows.create_volume [req-212b9fe5-9f4b-4969-aad3-16ad3eca78a7 8612ed5d8c794e9499bc2b6152bec6ad cc3dbcabf1d04bbd875f22f824dd0d5f - - -] Failed to run task cinder.scheduler.flows.create_volume.ScheduleCreateVolumeTask;volume:create: No valid host was found. No weighed hosts available