LaCie Biggest Quadra 1,5TB FW800 => upgrade to 4 * 2TD SSD

Sadly, I don’t know of anyone that can give you a definitive answer.

What I can tell you is the FireWire 800 interface doesn’t care what the data flow is coming from. The SATA ports the drives are using don’t care either. That only leaves the RAID application may not support the size of the drives and the total size of the RAID.

So what would I do?? First I would look for a second unit! I found one for $200 bucks Lacie Biggest Quadra Hard Drive Array Series - 4 bay - No Drives Included so now you can work it out on the spare unit with the SSD’s

Now let’s look at this in a slightly different way. As you know FireWire 800 is still not very fast considering Thunderbolt-3. But maybe having two units allows you to leverage both functionally doubling up the throughput!

I would limit the drives to only two bays so you could RAID either across the units or if one failed mount the other drives into the still working unit.

While you want to go with 2TB drives consider the 4 TB drives. Remember you’re still bottlenecked by FireWire so going across 4 drives in one unit won’t get any speed, 2 SSD drives will saturate the pipe.