Improvements

Rook v1.5.1 is a patch release limited in scope and focusing on small feature additions and bug fixes.

Ceph

Ceph-CSI updated to the latest v3.1.2 by default (#6676, @Madhu-1)
PDBs for OSDs redesigned to allow multiple nodes in a zone to drain (#6497, @sp98)
Snapshot scheduling for mirrored pools (#6553, @leseb)
Restore mon clusterIP if the service is missing (#6558, @travisn)
Multus support for CSI in a non-default namespace (#6396, @rohan47)
Add external cluster script to the toolbox (#6648, @leseb)