XenDesktop per-user and per-device licensing
XenDesktop has two major licence models: per-user/per-device and concurrent. Concurrent is simply based on the number of sessions running at any one time. Per-user/per-device is more complicated as licences may switch between per-user and per-device modes automatically. The good news is that the licence system can intelligently and dynamically reassign licenses between users and devices to make the most efficient use of the available licenses. For example, consider the following scenario for a brand-new environment where no licenses have yet been assigned:
- User 1 logs on from client Device 1. The license server will, by default, check out a license to User 1.
- User 1 logs off, and User 2 logs on from the same client device. The license server, now sensing that two different users have logged on from the same device, will take the license that was assigned to User 1, and reassign it to Device 1. Any subsequent users who log in from Device 1 will not cause any action by the license server, because Device 1 is already licensed.
- If User 1 logs on again from a different client device, the license server will again check out a license to User 1 (so, at this point, two licenses are checked out: one to Device 1 and one to User 1). Since User 1 has logged on from two different devices, the license will remain assigned to User 1 unless/until manually released by an administrator (e.g., in the case of the employee leaving the organization), or unless User 1 doesn’t log on for a period of 90 days, in which case it will be automatically released due to inactivity.
- Likewise, since two different users have logged on from Device 1, that license will remain assigned to that device unless manually released or automatically released due to 90 days of inactivity.
How do you know how many licenses you really need? There is a formula that will tell you that. You need to know how many total users you have (let’s call that number “U”), how many shared devices you have (let’s call that “D”), and how many of your users will use only shared devices (let’s call that “S”). The formula is U – S + D. So, if you have 1,000 total users, 300 shared devices, and 600 of your users will use only shared devices, you need 1,000 – 600 + 300 = 700 total licenses.
For more information on exactly how this works, see the Citrix Community Blog post by Christophe Catesson, which in turn links to a recorded session from Synergy 2011 that was a deep dive discussion of XenDesktop licensing.