For the sake of simplicity , is it possible to map somehow the free disk space on three servers into a single directory and have the filesystem handle the sharding?
I believe https://github.com/trapexit/mergerfs might be it but I find the documentation a bit terse and can't figure it out.
Following Gerald Schneider's comment since I already had a Docker swarm ongoing on my three hosts, I have used https://github.com/gongonpower/glusterfs-swarm successfully to set gluster up.
The only change necessary was, for this use case, the create command should be simply
gluster volume create gv0 gfsc1:/bricks/brick1/gv0 gfsc2:/bricks/brick1/gv0 gfsc3:/bricks/brick1/gv0
The repository uses "replica 3" which is not what we need here. Also, if you managed to create the wrong volume, after removing it to re-add the same bricks the --force argument needs to be added to the end of the next create command.