Open Directory vs Active Directory migration from Windows to Mac

You can't bind PCs to Open Directory without 3rd-Party help (pGina). Besides depending on the OS this may not work reliably? You'd have to trial it first. Beyond binding and providing a home folder there would be nothing else. No management, no policies etc from Open Directory to your PCs.

The supported way of doing this is to use Active Directory, and supplement it with OD for managing your mac estate only. Again you can't apply GPOs to macs without 3rd-Party help which can be very expensive.

Not that it's something you would consider - although you might do? It may be best to go 'all mac' if your intention is to move to macOS. If your PCs are using software that is only available for PCs consider using VMs on your Macs to keep that aspect of school going.

My 2p

Since you cannot apply GPOs to Macs in an AD environment and I guess (haven't tried it yet) Windows PCs would have similar problems in OS X Server environment, have you considered setting up a linux based server for both Macs and WinPCs during the migration to full macOS+Server environment?

Since you already have a Windows server which can act as a server both Windows and Macs I would stick with that. Also frankly Apple's server software is a bit of joke. (A bad one. 😟)

I am surprised that a year old server is allegedly running Windows Server 2008, clearly 2008 is much older than a year. It would have been more logical to have Windows Server 2012R2 which would have been the current version a year ago. I would suggest upgrading it to at least 2012R2 if not 2016.

I would agree managing Macs is best done via Mac tools. However this does not require specifically Open Directory as these days management is done via a Mobile Device Management solution (MDM) e.g. Apple's Profile Manager, or JAMF Casper Suite, or similar. Many of these can run on non-Mac servers, some can run on Mac servers, its your choice.

A MacBook Pro as a server which is what you apparently said would be a terrible idea as it would be a waste of an expensive laptop. If you really must use a Mac as a server then a Mac mini is the more common choice.

You could get two Mac minis for a similar price.

For the numbers we are talking about here, either 45 each or 90 total the bigger issue is going to be network bandwidth. Having two Macs means each handles half as many connections for the same bandwidth.

You could add either additional network interfaces to a single Mac, or even a 10Gbps interface to a single Mac, or as I suggested use two Macs. Another benefit of two Macs is that each also has their own storage and own connection to that storage again effectively doubling the 'speed' of the storage in total.

With regards to CPU power then basic file serving is not particularly CPU intensive, with regards to memory more is always better but a MacBook and Mac mini both can do the same amounts of RAM.

In fact the components in a Mac mini are very similar to a MacBook Pro so the performance really is quite similar.