REVIEW: http://review.gluster.org/15919 (cluster/tier: mask event generation on detach start) posted (#1) for review on master by Milind Changire (mchangir)
REVIEW: http://review.gluster.org/15919 (cluster/tier: mask event generation on detach start) posted (#2) for review on master by Milind Changire (mchangir)
Patch https://review.gluster.org/#/c/glusterfs/+/21331/ removes tier functionality from GlusterFS. https://bugzilla.redhat.com/show_bug.cgi?id=1642807 is used as the tracking bug for this. Recommendation is to convert your tier volume to regular volume (either replicate, ec, or plain distribute) with "tier detach" command before upgrade, and use backend features like dm-cache etc to utilize the caching from backend to provide better performance and functionality.