I've been saving my DVD collection as iso files on my server and then watching them on any of the TVs in the house using FUSE (ssh). Works great. But over the years I keep exceeding disk storage even though disks keep getting bigger and bigger. I'd add more disks to the server but it keeps getting smaller and smaller, which is a good thing. I have a 2TB drive now at 85% capacity with a 2TB USB back up drive. It occurs to me that if I but add another 2TB USB drive to the mix I could double my capacity by using a software RAID5 configuration. Before I leap I thought it wise to throw this idea out for a sanity check. Questions: 1) Am I correct that performance using wired ethernet (1G) and dual core (64bit) Linux/Mac computers as server/client computers will not be an issue? 2) If you are using a different approach to solve pretty much the same problem, what is your solution?
I'm not fully answering the question, but for RAID 5 you need three disks, not just two. Raid 0 (striping) would be possible with two disks and double your storage, but you will lose all your data if either of the disks fail. Additionally depending on what kind of RAID setup you have you might not be able to turn a non-raid disk into a raided disk without losing your data.
To somewhat answer your questions, I have a software RAID5 (using Windows) with four disks, and that is not able to max out a 1 gigabit network, so the network isn't an issue here. Additionally I'm doing this on a 64bit quad core Intel, but even though it is software RAID the CPU is no where near being maxed out.
Very soon I'm creating a new software RAID based on Linux's LVM or something similar. I haven't fully read up on it yet, but I plan to buy a small Atom based board, and make a very small NAS.