Edit (Mai 7th 2016) : im gonna cover Alternative datapaths for windows too very soon since i recently moved to Windows Reaper
its not that different from osx but it always helps to see the correct paths for understanding the patterns for those who struggle a little, i struggled my self in the beginning so i know exactly how that feels

external HHD`s can be used with great success on both windows and os x, even with sub folders
ok, we need a place to explain and share information on how to for nebula
so we can have it in one place rather than scrolling trough countless of Nebula tip of the Month
ill start with posting a copy of my xml file with path`s for external hdd
this xml is for mac osx
im a Logic Pro X user so its the Nebula3 x64.xml you should start with within the component folder if you use Logic Pro X
if it does not make sense just ask
its all about the ALTERNATIVEDATAPATH
but you should first look at your own xml file located in component folder if you use logic and see whats different
thats the way i did it the first time
MAKE A COPY OF YOUR XML FILE BEFORE YOU MAKE ANY CHANGES TO BE ON THE SAFE SIDE
when you have successfully gotten this to work with the regular nebula xml
you can do the same with the reverb version
but once you understand this you may want to organise your folders within the main nebula libraries folder different than i did it, thats totally up to you
WARNING!!!
INIT.N2P and INIT.N2V must not be deleted,
so you can not delete Vector and Program folders where nebula is installed as those files need to stay in there
everything else in vector and Program folders in the nebula directory should not be a problem to remove and be placed on external HDD
ITS ABSOLUTE IMPORTANT NOT TO DELETE
INIT.N2P and INIT.N2V
WITHIN NEBULA AFTER REMOVING YOUR LIBRARIES FROM THESE FOLDERS VECTOR AND PROGRAM