Why are two gluster FS processes spawned for a single gluster mount?

Issue

• When reviewing the output of the pscommand, there are two glusterfs processes bound to a single gluster mount.

• Taking a persistent volume created for a postgresql pod as an example, the following gluster mount of volume vol_8392ee620beb8d97d4e28ea18f669290

  1.2.3.4:vol_8392ee620beb8d97d4e28ea18f669290 on /var/lib/origin/openshift.local.volumes/pods/d7babab7-292b-11e9-a72e-fa163e6bed00/volumes/kubernetes.io~glusterfs/pvc-c5c9afef-292b-11e9-a72e-fa163e6bed00 type fuse.glusterfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other,max_read=131072)
  

  has two matching glusterfs processes running:

      root      39512  0.0  0.0 148764   732 ?        Ss   04:53   0:00 /usr/sbin  /glusterfs --log-level=ERROR --log-file=/var/lib/origin/openshift.local.volumes/plugins/kubernetes.io/glusterfs/pvc-c5c9afef-292b-11e9-a72e-fa163e6bed00/postgresql-1-pxvn7-glusterfs.log --fuse-mountopts=auto_unmount --volfile-server=1.2.3.4 --volfile-server=1.2.3.5 --volfile-server=1.2.3.6 --volfile-server=1.2.3.7 --volfile-id=vol_8392ee620beb8d97d4e28ea18f669290 --fuse-mountopts=auto_unmount /var/lib/origin/openshift.local.volumes/pods/d7babab7-292b-11e9-a72e-fa163e6bed00/volumes/kubernetes.io~glusterfs/pvc-c5c9afef-292b-11e9-a72e-fa163e6bed00
  
      root     39513  6.2  0.3 614184 31248 ?        Ssl  04:53   0:05 /usr/sbin/glusterfs --log-level=ERROR --log-file=/var/lib/origin/openshift.local.volumes/plugins/kubernetes.io/glusterfs/pvc-c5c9afef-292b-11e9-a72e-fa163e6bed00/postgresql-1-pxvn7-glusterfs.log --fuse-mountopts=auto_unmount --volfile-server=1.2.3.4 --volfile-server=1.2.3.5 --volfile-server=1.2.3.6 --volfile-server=1.2.3.7 --volfile-id=vol_8392ee620beb8d97d4e28ea18f669290 --fuse-mountopts=auto_unmount /var/lib/origin/openshift.local.volumes/pods/d7babab7-292b-11e9-a72e-fa163e6bed00/volumes/kubernetes.io~glusterfs/pvc-c5c9afef-292b-11e9-a72e-fa163e6bed00
  

• It's worth noticing that the PIDs are consecutive in numbering.