diff --git a/doc/releases/mimic.rst b/doc/releases/mimic.rst
index 1fd93e8f7c4..bcffe5d3319 100644
--- a/doc/releases/mimic.rst
+++ b/doc/releases/mimic.rst
@@ -69,6 +69,36 @@ Notes
 Instructions
 ~~~~~~~~~~~~
 
+#. If your cluster was originally installed with a version prior to
+   Luminous, ensure that it has completed at least one full scrub of
+   all PGs while running Luminous.  Failure to do so will cause your
+   monitor daemons to refuse to join the quorum on start, leaving them
+   non-functional.
+
+   If you are unsure whether or not your Luminous cluster has
+   completed a full scrub of all PGs, you can check your cluster's
+   state by running::
+
+     # ceph osd dump | grep ^flags
+
+   In order to be able to proceed to Mimic, your OSD map must include
+   the ``recovery_deletes`` and ``purged_snapdirs`` flags.
+
+   If your OSD map does not contain both these flags, you can simply
+   wait for approximately 24-48 hours, which in a standard cluster
+   configuration should be ample time for all your placement groups to
+   be scrubbed at least once, and then repeat the above process to
+   recheck.
+
+   However, if you have just completed an upgrade to Luminous and want
+   to proceed to Mimic in short order, you can force a scrub on all
+   placement groups with a one-line shell command, like::
+
+     # ceph pg dump pgs_brief | cut -d " " -f 1 | xargs -n1 ceph pg scrub
+
+   You should take into consideration that this forced scrub may
+   possibly have a negative impact on your Ceph clients' performance.
+
 #. Make sure your cluster is stable and healthy (no down or
    recoverying OSDs).  (Optional, but recommended.)
 
@@ -177,7 +207,9 @@ Upgrading from pre-Luminous releases (like Jewel)
 -------------------------------------------------
 
 You *must* first upgrade to Luminous (12.2.z) before attempting an
-upgrade to Mimic.
+upgrade to Mimic.  In addition, your cluster must have completed at
+least one scrub of all PGs while running Luminous, setting the
+``recovery_deletes`` and ``purged_snapdirs`` flags in the OSD map.
 
 Upgrade compatibility notes
 ---------------------------