Automounting Volumes on OS X Revision as of Sunday, 27 December 2015 at 07:27 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