I have FreeNAS 11.3 joined to an AD environment with over 50,000 users. At first this was too much for FreeNAS, but after checking "Disable FreeNAS Cache" most users haven't had any issues. However, a few newer users are having inconsistent permission issues. Permissions are managed by groups. Even though the new user gets added to the correct group and in FreeNAS command line I can "id username" and confirm FreeNAS is seeing them in the right group, they get permission errors when mounting...
Large AD inconsistent permission issues
Large AD inconsistent permission issues