We have about 15 OS X desktop machines - mainly iMacs, some MacBooks and Mac Pros. Each user has a local account on the machine, and a portable USB disk for a Time Machine backup.
I want to coordinate the backups to a central NAS, and I'm thinking about something like the Synology DS2411+ (I know there are only 12 bays; we may need 2 of them!), allocating one disk each for each client machine.
Our network hardware is gigabit capable, and all clients connect at 1000baseT. I'm concerned about the network utilisation. I know the initial full backup will take a long time, but I'm prepared to do that one machine at a time overnight. But what about when multiple clients do their incremental TM backups at the same time? What kind of impact could that have on the network?
Is this a feasible network based solution? Are there alternatives?
Yes, this is feasible, but it might take some hackery to get it working. As far as I know, the only officially supported (read: easy-to-implement and stable) network TM backup is when backing up to either a Time Capsule or an OSX Server.
It is possible, though, to back up to an afp or smb share - just don't depend on it being reliable. I had it working for a while at home and it needed constant prodding to get backups working.
I'm actually using a network TM backup strategy for our office. We have a smaller office than yours (7 MBPs/iMacs) backing up to a central server over gigabit ethernet. Network IO doesn't seem to be an issue throughout the day.
I know my incremental backup tends to be a few hundred megs a couple times a day. Over gigabit, this is really a non-issue, just a few minutes of network traffic. Once a week my backup is around 10GB, which takes a little longer. I've noticed that under the big backups, if I'm utilizing a lot of system resources, my system slows down significantly while doing the backup. I expect this is due to the slow hard drive we're using as a backup device and my system is trying to write data over the network, and it's just not being written on the other end fast enough.
My backup server is a Ubuntu box, and I allocate 200GB for each user to backup. The drive situation isn't as robust as I'd like (1 single 7200 RPM drive in a RAID1) but it's alright for now. There's some tutorials on how to get this to work, it's a big of a pain to set-up but it seems like it's working alright for everyone. The solution uses Netatalk and AFP, and there're some tutorials out there on how to get it to work this one is pretty comprehensive and it has a lot of user comments. It is the one I used to get our system set up.