failure to mount smb (cifs) drives

On a newish lenovo ThinlCenter M75-s machine, running Mga7, I'm having a lot of difficulty in mounting these drives on boot-up/ The cifs units are a pair of Drobo NAS units. I've been using these for some years from another machine, but this one seems to fail all the time. The /etc/fstab entries are identical, but they do not mount, at least not before the boot sequence moves on, registering a failure to mount. Mounting manually, after the boot sequence, works without problem, from the command line, logged in as root. the Drobo units are characterid=sed by 'going to sleep' if not being addressed. A factor that Drobo inc have recognised long ago, and the introduction of the 5n2 unit, which incorporates an optional SSD for a quick wakening. It'ss till a bind, however, that at every boot, the mount fails. It's not that the boot sequence has not had time,. booting hangng for a minute and 45 seconds on this aspect, which makes the boot-up somewhat longer than it would be on my main desktop unit.