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One of my friends controls hundreds of Macs for a school. They have Lion.

The 6th grade Macs have the 6th grade accounts (~100), the 7th grade Macs have the 7th grade accounts (~120) and the 8th grade Macs have the 8th grade accounts (~90). There are also some staff accounts.

He doesn't have all the users on all the Macs; I believe that he has them set up to grab the profiles from a server - thus, a user's desktop on one computer is synced with that user's desktop on another computer.

I'm wondering whether or not it's possible to put all ~400 users on each computer so that the grades can use each others' Macs interchangeably. Is it possible to put this many users on a Mac? And how many of these can be logged in at the same time?

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I'm wondering whether or not it's possible to put all ~400 users on each computer so that the grades can use each others' Macs interchangeably

Most certainly. I'm at a university where they do this on a much larger scale (think about 10–20k), so 400 should be possible — but, it also depends on the school's IT infrastructure. The user directories and settings are all on a central server (or perhaps server farm, I don't know) and each machine pulls the info when you login. You can login from any machine anywhere in the campus.

Typically, the maximum number of accounts the server can have is limited by the storage space, and the number of simultaneous logins are typically limited by the amount of memory, processing power available and network bandwidth (the clients need to communicate with the server and a single server can only process a certain number of requests at a time). So a definite answer is hard to provide.

The general approach is to spread the load (when demand spikes) over a cluster of servers or a server farm such that the end-user performance remains the same. Of course, no one expects the entire campus to be connecting all at once (there probably aren't enough machines for that). You can read more load balancing here.

This discussion mentions a software enforced default limit of 1024 simultaneous connections, extendable up to 2048. If you find yourself running at the far end of this limit, then you're either not balancing your load properly or you're under equipped.

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Do you know the software limit? – JavaAndCSharp Apr 2 '12 at 2:29
@JavaAndCSharp See my edit – R. M. Apr 2 '12 at 2:54

I would imagine they're using something like Open Directory - so really, it's not all the users on all the Macs, but all the users on a central server that controls access to all the Macs. Also, central control of home directories and such, so each Mac is really just a node for people to log onto and use their shared infrastructure.

It's very hard to control such infrastructure with hundreds of users without centralization.

The limit is in the thousands - 200,000 database items I believe, although that's not users, but includes servers, Mac, etc.

With a centralized Open Directory system running from an OS X Server you can handle all 400 users from one central server. Best to have a couple for resiliency, etc.

Add to this that there are considerations of usage, network design, etc. that also come into play. In some scenarios you might want 1 server (or server pair) per grade if you're split into individual computer labs or similar. Then take a look at the network topology and work out how much data is expected to flow over individual links, etc.

That link quotes 1000 simultaneous clients connected. Remember that's running from a central server, not on any given Mac. You expect only one user at a time on any given Mac.

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