I might be interested in one of them, but I have a few technical questions first.
If I have two 1U servers on the same subnet (each with three 750GB) and in the same group, if I needed more capacity must I add a 4th disc to each of the servers? Or could I get by just adding one disc to one of the servers and leaving the other with an empty slot?
I believe you can add only a 4th disc to either one of the 1U servers, that will give you the additional space provided by that 1 disk. The answer is yes, you can get by just adding one disk to one of the servers and leave the other empty.
So if I add a 1TB to a server with three 750GB, I gather I only gain 750GB extra capacity for content, and an extra 250GB for parity? How would that 250GB for parity ever be used when the largest disc for content is 750GB?? I just don't understand that bit.
If you had 3 x 750GB on a 1U and you added an additional 1TB, that additional 1TB you have just added now becomes a parity drive, and the 750GB that was previously a parity drive will now be freed up to be used for storage.
When I've got two 1U servers in a group like this, does each server have a 750GB disc set aside for parity, or is only one 750GB used for parity and all the others for content? Can I swap discs between servers in a group?
I believe each 1U chassis requires their own parity drive. Meaning to say if you had 10 1U servers clustered together in the same group, you would have 10 parity drives - 1 each in each server chassis. No, you can't swap singular disk drives between servers, but you can swap disk sets between servers. For example, if you took the hard disk out of Server 1 Slot 2 and put it into Server 2 Slot 4, I don't think it'll work. But if you took all the hard disks from Server 1 and put all of them into Server 2, that won't be a problem. Drives are married together, but the drives and the chassis aren't.
Or, being mindful of capacity requirements with BluRay when M500Mk2 and Vault get released. Should I just replicate all my content from both servers onto the one server with three new 2TB discs, leaving me with 6 surplus discs and an empty server that I can sell?
I think its really your call, depending on the amount of content (including Blu-rays) you intend to store. Bear in mind that 1 Blu-ray = 6 DVDs (approx.), a 1U fully loaded with 2TB disks could get you 900 DVDs, but only 150 Blu-rays. If you are intending to store more Blu-rays, I would suggest for you to keep the server and purchase additional drives as and when necessary. Sell the surplus disks, keep the server. My 2 cents.