I'm seeing similar warning messages too since upgrading from jessie to stretch: "WARNING: Failed to connect to lvmetad. Falling back to device scanning."
Apparently, use_lvmetad was changed from 0 to 1 in lvm.conf going from jessie to stretch, but lvm2-lvmetad.service is disabled. Should I enable lvm2-lvmetad.service or set use_lvmetad to 0? Best, David
