[Bugs] [Bug 1529768] New: Disk size is incorrect according to df when an arbiter brick and data brick live on the same server

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1529768

            Bug ID: 1529768
           Summary: Disk size is incorrect according to df when an arbiter
                    brick and data brick live on the same server
           Product: GlusterFS
           Version: 3.12
         Component: arbiter
          Severity: medium
          Assignee: bugs at gluster.org
          Reporter: ben.edgar at appian.com
                CC: bugs at gluster.org



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:

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