I run a 13 rMPB on Mavericks. Under the previous system, I used Thunderbolt to FireWire to a daisy chain of six LaCie drives, 4 Quadra d2 and 2 Porsche. I use one of the drives for my entire iTunes Library and one for my TimeMachine backup so those two drives at least are absolutely critical to me.
As soon as I upgraded I began to have problems. Drives would appear on the desktop but when I'd double click on them, they wouldn't respond. I would force restart and the drives wouldn't appear at all. In the past I had used Disk Utility to rebuild the directories and I did that repeatedly.
Ultimately, I have done these things:
(a) I have turned off the Energy Saver toggle telling the system to spin down the drives when not needed. This seems to conflict with LaCie's own energy save software. The LaCie functionality still works and the drives do now spin up when needed.
(b) When I shut down, I turn the drives off at the on/off switch. When I restart, I turn the drives back on. I had run into cases in the past where the drives would disappear if I'd had to force shutdown for some reason; turning them off and on always fixed the problem. Now I do it every time.
These two steps, while tedious, seem to have solved the problem for me. Except:
If I every have to restart (as for example with a system upgrade), I anticipate that after the restart I will need to force shutdown, turn off the drives, turn the drives back on and start up. This is concerning but so far so good.
I have been back and forth with LaCie tech support. I'm sympathetic to their plight but so far they haven't been all that helpful. There is a firmware update available for both the Porsche drives and the Quadra D2 drives but I haven't been able to make it work and it requires interacting at the terminal. LaCie's latest suggestion was that I find a Mac with a FireWire port and connect the drives to that machine to do the upgrades. Unfortunately, that won't work since I only have the one machine.
In the meantime, steps (a) and (b) above are working ok enough that I can go on with my life until this all settles out.
HTH.