Bug 1529768

Description of problem:
When this new feature was released in 3.12 (https://github.com/gluster/glusterfs/blob/release-3.12/doc/release-notes/3.12.0.md#enhanced-the-option-to-export-statfs-data-for-bricks-sharing-the-same-backend-filesystem), now the "df" command is incorrect when listing the available disk space on a server that has one data brick and one arbiter brick.

The arbiter brick should not take up as much space as a data brick since it only contains file metadata, so the actual equation for calculating total space on a server should be: total-space / number-of-data-bricks-at-node, instead of total-space / number-of-bricks-at-node.


Version-Release number of selected component (if applicable):
3.12

How reproducible:
Always

Steps to Reproduce:
1. Create a volume with an arbiter brick and data brick on the same server
     gluster volume create <vol-name> transport tcp replica 3 arbiter 1 server1:/data-brick server2:/data-brick server1:/arbiter-brick
2. Mount the volume on any server
     mount -t glusterfs server1:/<vol-name> /mounted-volume-path
3. Run "df -h" and see that the "Size" column is only half of the total underlying filesystem size instead of the entire underlying filesystem size because a data brick and an arbiter brick reside on the same server.

Actual results:
The Size column shows half of the total size of the underlying filesystem when an arbiter brick and data brick live on the same server.

Expected results:
The Size column should show the total size of the underlying filesystem when an arbiter brick and data brick live on the same server.

Additional info: