Regarding filesystems and shared access:
On the client side, DOS just sees a mass storage device that uses 512 byte sectors. The filesystem to be used depends on the DOS version and the size of the image, but it's always going to be some variant of FAT because this is DOS. By implementing NetDrive as a block device driver I was able to get it to run on all versions of DOS that support installable device drivers without having to do things like make it aware of the DOS version number or play with non-documented DOS data structures. It just works.
On the server side it's just a file that is an image of the partition. The server side doesn't know or care whether it is FAT12, FAT16 or FAT16B - it's just 512 byte reads and writes into a file, and it really has no idea of what is in that file. If there were clients for Amigas or other machines the server would be fine. (I need to make the sector size variable, as right now it assumes 512 byte Sectors.)
There is no concurrent access allowed because that would be logically equivalent to two machines trying to write to the same (virtual) hard drive; the machines don't know about each other so that is just going to cause corruption. The only exception is read-only access; two machines can use and access a single image on the server if that image is marked as read-only.
The server side can also send new writes to a journal file. This is used to implement the "undo" feature - imagine you make a mistake and delete something you needed, or you made a configuration change or installed software and then you changed your mind. NetDrive allows you to go back in time and undo those changes, right from the DOS command line. I don't know of any other shared filesystem or network attached storage for DOS that can do that.
For public facing servers I implemented a party trick that allows multiple clients to connect to the same image and do writes. It also uses journal files, but in this case instead of having one journal per drive image there is a shared drive image and one journal per open client. The writes from a client go to its journal file, making those writes private to the client. This gives the clients the illusion of having a read-write drive letter. (The writes for that client disappear when the client disconnects, and the underlying image never gets modified.)
Regarding TCP, IP and UDP:
While I grew up on DOS 2.1, I was also exposed to Unix decades ago and that's why I started with the classic Unix programs first - FTP and Telnet in particular. NetDrive is actually only using UDP, not TCP, but the IP configuration that you speak of is required for both. Even with UDP and IP in the device driver the executable code in the driver is less than 3KB in size; most of the rest of the 6KB of used space is for an incoming packet buffer and three stacks, which are needed to make it reliable across a range of DOS versions. DHCP does make client configuration much easier and my servers rarely move so accessing my servers by name works well and I don't care what address the clients are temporarily using.
Using IP and UDP makes it routable, which is a feature I really like - any DOS machine in the world can access a server running on the Internet, which is a neat party trick. For a proof-of-concept I have an almost complete copy of the SIMTEL archive available on a public NetDrive server. Instead of FTPing to it, grabbing a file, and then unzipping it locally you can literally connect to it as a drive letter, find something you like, unzip it right on the server, run it from the server, and decide if you like it or not. If you don't like it you can delete it or just go try something else. It's not as fast to transfer data as FTP is, but for DOS users it's a more natural way to interact with a downloads section. While the proof of concept works, I've not publicized it because the speed is highly dependent on proximity to the server. I have code that fixes that, but it's stalled waiting on other things.
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NetDrive is closer to a Zip drive that you move around than a shared filesystem. One machine accesses it at a time, and the only way to share is to move the drive to another system. But because it is software and it is using networking, that can happen in seconds and without rebooting. And you can add anywhere from 10MB to 2GB per drive letters, and up to 24 drive letters. And that virtual Zip drive can be in Alberta Canada while you sit in California. And it has an undo feature, and a few other tricks.