One of my servers is 90% full - that means I need to upgrade it from 2tb volumes to 4tb before it hits 100%. I was using 2tb volumes because fdisk-type partitions can't cope with 4tb, but there's a new type of partition, the GPT, and that can, so with a more recent version of Linux, I can have these bigger partitions.
I'm also going to try using 3tb drives - I've read that some motherboards can't handle them, so I'm going to get just one, to experiment with. 3tb drives are now the same price-per-byte as 2tb, so they're now a sensible buy.
I'm also going to make my first foray into SSD (solid state drives). They're much faster than mechanical drives, and because they don't have moving parts, I can hope they'll be less failures. I'm going to use 16gb SSDs for the system drive - SSD is far too expensive to use it for mass data storage. So I've ordered the SSDs, they come in at about $40 (£25) for a 16gb drive. We'll see how that goes. I also ordered ten 4-port Sata cards; they'll be needed to make the beefier servers. I got them for $15 (£10); I've been paying £25, so I'm hoping that these cheaper ones actually work! Bluepoint offer 30gb SSDs for £33, so I might also try those.
So, I'm planning to make four servers. Three of the "small" ones, with 4 2-tb drives, and one of the larger, with a 3tb and 5 2tbs. I already had 4 2tbs in stock, so I'll need to order 14 more, plus the 3tb.