Recommend you consult [https://github.com/gboudreau/Greyhole/wiki/WhatNotToPutInGreyholeShares what not to put in Greyhole shares] as a precaution when determine which shares will be Greyhole enabled.  You can add additional drives to your HDA and prepare them for use in Greyhole by following [[Adding_a_second_hard_drive_to_your_HDA|adding a second hard drive to your HDA]] guidanceor use the Amahi [https://www.amahi.org/apps/disk-wizard Disk Wizard] (Amahi 8 or greater).