Feat: Add volume commands to show total available space and per-node brick usage

[SpiderUnderUrBed]

GlusterFs should provide commands to see how much storage is being used per node, and the total available space a volume has, df does not work with this, and frequently encounters bugs or intended behavior where either the smallest node storage limits is shown, so a purpose made tool would be more reliable, and there should be a command to see per node usage of storage space as its useful for several reasons, like debugging some storage issues. This is better than sshing into each node and running du or df (if you allocated a whole partition).

There was a issue about total available space: #601but it was auto-closed, I assume the bot wont auto-close discussions so I am making this here for better visibility.

[ThalesBarretto]

Can you write an rfc patch for that functionality?

[SpiderUnderUrBed]

@ThalesBarretto
I am not against writing an RFC, I will be able to write it at November or later due to some stuff happening right now, but I am not the best person to write an RFC as I am a few days new to using glusterfs and have no familiarity with the project, you are a contributor and would be better suited to write an RFC, however if you dont have time or just dont want to write an RFC which is fine, I just want to know:

• Do i make it in discussions or issues?
  and
• There is no expectation of me contributing code, because I would probably be ill suited to contribute to glusterfs

Also would it be worth adding to the discussion the ability for glusterfs to appear as the full available size and not just the smallest node space when running tools like df -h in the mount point (upon researching I think this is an intended feature rather than a bug)