The only supported and official way of running clvmd and cmirrord daemon in
CentOS7 is to have these daemons managed by cluster resource manager directly
(e.g. using the pacemaker) instead of running it as a system service defined
by an initscript or a systemd unit. Therefore, the lvm2-cluster (where clvmd
daemon is packaged) and the cmirror package (where cmirrord daemon is packaged)
now requires the resource-agents package which contains a resource named 'clvm'.
The clvm resource provides both clvmd and cmirrord daemon management.
The cmirrord is an optional part of the clvm resource and it can be enabled
by using 'with_cmirrord=1' parameter when setting up the this resource.
See the clvm resource description for more information (e.g. by running
'pcs resource describe ocf:heartbeat:clvm')

Although there is still a possibility to run the clvmd and cmirrord daemon
as a standalone system service without a need for cluster resource manager,
such a setup should be used for testing purposes only and it should not
be used in production. For this scenario, the new and optional packages called
lvm2-cluster-standalone and cmirror-standalone contain respective systemd
units to run clvmd (via lvm2-cluster-activation.service) and cmirrord
(via lvm2-cmirrord.service) as standalone system services without cluster
resource manager involvement.