Document URL: 
-- app storage part 
https://access.redhat.com/documentation/en-us/red_hat_openshift_container_storage/3.11/html/deployment_guide/chap-documentation-red_hat_gluster_storage_container_native_with_openshift_platform-upgrade#chap-Documentation-Red_Hat_Gluster_Storage_Container_Native_with_OpenShift_Platform-Upgrade-Gluster_pods

-- registry-storage
https://access.redhat.com/documentation/en-us/red_hat_openshift_container_storage/3.11/html/deployment_guide/chap-upgrade-glusterfs-registry-namespace#chap-registry-Documentation-Red_Hat_Gluster_Storage_Container_Native_with_OpenShift_Platform-Upgrade-Gluster_pods

Section Number and Name: 
app-storage:
6.1.3. Upgrading the Red Hat Gluster Storage Pods
   11. Execute the following commmand and ensure that the bricks are not more than 90% full: 
                 # df -kh | grep -v ^Filesystem | awk '{if($5>"90%") print $0}'

registry-storage:
6.2.3. Upgrading the Red Hat Gluster Storage Registry Pods
   10.  Execute the following commmand and ensure that the bricks are not more than 90% full: 
                 # df -kh | grep -v ^Filesystem | awk '{if($5>"90%") print $0}'

Describe the issue: 
I think we should explain better why this step is needed, what could happen if ignored and most important what to do if one is beyond the limit

Suggestions for improvement: 
Elaborate the reason for this check as well and consequences if ignored _and_ what to do if bricks are fuller than the 90%

Additional information: