The size of the privat folder

WD Legacy Products My Book Live
2

That’s weird any private folder that you create should have access to the complete capacity of the MBL. Check if the link below helps to solve your problem. 

http://community.wdc.com/t5/My-Book-Live/How-can-I-increase-private-folder-size-Default-is-17-4GB/m-p/305556/highlight/true#M6616

You can also try to map the folder with WDlink. 

http://wdc.custhelp.com/app/answers/detail/a_id/8573/session/L3RpbWUvMTM1NDIyMzQzOS9zaWQvTXBOa2d3Y2w%3D