To configure Mac OS X to automatically mount a Drobo FS share whenever it is accessed:

Add the following line to /etc/auto_master:

/Volumes/Drobo                      auto_drobo

Then (as root) create the file /etc/auto_drobo and add your mounts to it, e.g.

Share1 -fstype=smbfs ://username1:password1@192.168.1.2/Share1
Share2 -fstype=smbfs ://username2:password2@192.168.1.2/Share2

Use the following command to start the automount:

/usr/sbin/automount -vc

Now whenever the volume is accessed it will be automatically mounted.

You might also want to change the default automount timeout setting which is in /etc/autofs.conf.