Incorrect local disk storage value reported by nova

Issue

• We noticed that computes local disk storage (used for ephemeral disks) reported is incorrect as it seems that it takes into account the NetApp storage used for volumes.

• We cannot create ephemeral disks as nova considers that local storage is full as you can see below, there's more used storage than available storage:

(overcloud) [stack@undercloud:~]$ openstack host show overcloud-compute-0.localdomain
+----------------------------------+----------------------------------+-----+-----------+---------+
| Host                             | Project                          | CPU | Memory MB | Disk GB |
+----------------------------------+----------------------------------+-----+-----------+---------+
| overcloud-compute-0.localdomain  | (total)                          |  32 |    261613 |     111 |
| overcloud-compute-0.localdomain  | (used_now)                       |  14 |     18432 |     393 |
| overcloud-compute-0.localdomain  | (used_max)                       |  14 |     14336 |     393 |
| overcloud-compute-0.localdomain  | bfce108949724b2589c0c87f95babaee |   5 |      5120 |     150 |
| overcloud-compute-0.localdomain  | 24c75b45b1ff48f8a648550b9c60a1b0 |   8 |      8192 |     240 |
| overcloud-compute-0.localdomain  | 49f0410632c14b02b197ece3c35d84b9 |   1 |      1024 |       3 |
+----------------------------------+----------------------------------+-----+-----------+---------+

[heat-admin@overcloud-compute-0 ~]$ df -hT
Filesystem                      Type      Size  Used Avail Use% Mounted on
/dev/sda3                       xfs       112G   14G   99G  13% /
devtmpfs                        devtmpfs  126G     0  126G   0% /dev
tmpfs                           tmpfs     126G     0  126G   0% /dev/shm
tmpfs                           tmpfs     126G  6.6M  126G   1% /run
tmpfs                           tmpfs     126G     0  126G   0% /sys/fs/cgroup
tmpfs                           tmpfs      26G     0   26G   0% /run/user/1000
tmpfs                           tmpfs      26G     0   26G   0% /run/user/975
storage-host:/nfs_export nfs4      4.8T  312G  4.5T   7% /var/lib/nova/mnt/559895e6d759941da864856debfb89f0

(overcloud) [stack@undercloud:~]$ openstack host show overcloud-compute-1.localdomain
+----------------------------------+----------------------------------+-----+-----------+---------+
| Host                             | Project                          | CPU | Memory MB | Disk GB |
+----------------------------------+----------------------------------+-----+-----------+---------+
| overcloud-compute-1.localdomain  | (total)                          |  32 |    261761 |     111 |
| overcloud-compute-1.localdomain  | (used_now)                       |  14 |     18432 |     366 |
| overcloud-compute-1.localdomain  | (used_max)                       |  14 |     14336 |     366 |
| overcloud-compute-1.localdomain  | bfce108949724b2589c0c87f95babaee |   4 |      4096 |     120 |
| overcloud-compute-1.localdomain  | 49f0410632c14b02b197ece3c35d84b9 |   2 |      2048 |       6 |
| overcloud-compute-1.localdomain  | 24c75b45b1ff48f8a648550b9c60a1b0 |   8 |      8192 |     240 |
+----------------------------------+----------------------------------+-----+-----------+---------+

[heat-admin@overcloud-compute-1 ~]$ df -hT
Filesystem                      Type      Size  Used Avail Use% Mounted on
/dev/sda3                       xfs       112G   14G   99G  12% /
devtmpfs                        devtmpfs  126G     0  126G   0% /dev
tmpfs                           tmpfs     126G     0  126G   0% /dev/shm
tmpfs                           tmpfs     126G  6.7M  126G   1% /run
tmpfs                           tmpfs     126G     0  126G   0% /sys/fs/cgroup
tmpfs                           tmpfs      26G     0   26G   0% /run/user/975
storage-host:/nfs_export nfs4      4.8T  312G  4.5T   7% /var/lib/nova/mnt/559895e6d759941da864856debfb89f0
tmpfs                           tmpfs      26G     0   26G   0% /run/user/1000