PersistentVolumeClaim for glusterfs storage in pending state due to "Server busy" error

Issue

• A newly created PersistentVolumeClaim (PVC) stays in Status: Pending.

• Examining the Status: Pending PVC, there are events like:

  Events:
    Type     Reason              Age                From                         Message
     ----     ------              ----               ----                         -------
    Warning  ProvisioningFailed  2m (x64 over 17m)  persistentvolume-controller  Failed to provision volume with StorageClass "glusterfs-storage": failed to create volume: failed to create volume: Server busy. Retry operation later.
  

• Looking into heketilogs, there are messages with Too Many Requests and operations in-flight (8) exceeds limit (8):

  [heketi] WARNING 2019/11/19 11:49:52 operations in-flight (8) exceeds limit (8)
  [negroni] Completed 429 Too Many Requests in 800.958µs
  [negroni] Started POST /volumes
  [heketi] WARNING 2019/11/19 11:49:52 operations in-flight (8) exceeds limit (8)
  [negroni] Completed 429 Too Many Requests in 182.937µs
  [negroni] Started POST /volumes
  [heketi] WARNING 2019/11/19 11:49:52 operations in-flight (8) exceeds limit (8)
  [negroni] Completed 429 Too Many Requests in 282.027µs
  [negroni] Started POST /volumes
  [heketi] WARNING 2019/11/19 11:49:52 operations in-flight (8) exceeds limit (8)
  [negroni] Completed 429 Too Many Requests in 286.491µs