Unix and Windows ACLs are mutually exclusive, this means that you must select the correct type of ACL to match the share; see the paragraph below the table for more details
When in doubt, or if you have a mix of operating systems in your network, select Unix ACLs as all clients understand them. Windows ACLs are appropriate when the network contains only Windows clients and are the preferred option within an Active Directory domain. Windows ACLs add a superset of permissions that augment those provided by Unix ACLs. While Windows clients also understand Unix ACLs, they won't benefit from the extra permissions provided by Active Directory and Windows ACLs when Unix ACLs are used.
NOTE: if you change your mind about the type of ACL, you do not have to recreate the volume. That is, existing data is not lost if the type of ACL is changed. However, if you change from Windows ACLs to Unix ACLs, the extended permissions provided by Windows ACLs will be removed from the existing files.