Gluster users - Nov 2019 - Issues occurred to start glusterfsd with no free space brick

Hello experts,

I had several troubles to start glusterfsd. I found an issue that many
glusterfsd processes are high load. Also a 'sync' command was hung-up,
but I didn't see an I/O error. I could not find the root cause, and I
decided to reboot the OS.
However, one of volumes failed to start. Also I found a fact that the
brick of the glusterfsd doesn't have free space.

Here, I have a question. If the brick is completely no free space,
can't the volume start?

So, I tried to make some free space, I directly removed some files
under the brick directory. But, the files had a hard link in hidden
directory ".glusterfs" in brick directory. I didn't know this
architecture. Thus, some files ought be currently existing in only the
".glusterfs" directory. I don't remember the inode number for
removed
files. I'm understanding this way irregular.

Fortunately, I could start the volume without error. But anyway now,
there are inconsistency from the glusterfsd. I have the other question
here. How can I fix this volume?

Best regards,
Kondo