You are losing me with this last statement. Why would you need 60 permanent connections? What are these three directories per station?
That's ok, O-P. Probably my poor English. If I have a network with 20 PCs and I want to backup 3 directories/folders from every PC I will have to permanently share 60 directories/folders. This is how I understand it.
The other issue is:
What will happen if the pc(s) get switched of in the evening and switched on in the morning? Some don't run on the weekend? Would I need to "mount -a" every morning to make sure all permanent shares are seen?
I have two partitions for my backups. They are never mounted except when a backup is to be performed, or a recovery needed. procedure is;
1. mount a backup partition
2. run backup or recovery process
3. unmount partition
Whether the partition being mounted is on a server, or a local drive, doesn't change anything.
Even if you connect to each station continuously, I'm still seeing only 20 mounts. one per station. The three directories being backed up would only need to be backed up to a single directory per station on the backup partition, and would not require a separate mounting for each. They are directories, not partitions, and backups, not shares. Why would you want to share backups?
I can backup my entire system, thousands of directories and files, over a single, temporary, mount/connection. So again I say, your logic is eluding me when you mention 60 permanent connections in fstab.