[donavanm]

+1, in general. To adda bit of content:

1) Power Hungry, the total power envelope of a rack position is the limiting issue. You can fit 16-20 disks per RU no problem. The constraint on total density is your 5kVa or 10kVa power budget. Watts matter.

3) sensitive to vibration, be very very quiet http://www.youtube.com/watch?v=tDacjrSCeq4

4) Density, actually 4TB is hitting the sweet spot for $ per byte last time I looked. If you need absolute density look for 5 & 6TB Real Soon Now. If you can tolerate some loss variable density disks around 5TB look quite a bit more cost effective.

5) Read ahead, you only need to read ahead by a couple of chunks. For video ball park it at 2MB. You don't really need lots of RAM, think 32-64GB per chassis. Additionally each 8GB dimm costs about the same power as a disk. By going with 32GB instead of 64 I can fit another 2-3 disks in the power budget per chassis.