Automounting Volumes on OS X Revision as of Sunday, 20 December 2015 at 19:56 UTC
OS X (client) will only mount external drives on user login (and not
reboot). To correct this,
sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool true
This creates a file:
/Library/Preferences/SystemConfiguration/autodiskmount.plist