But as he is only concern on reliability, Savvio is a good choice. Actually LTO/DLT should be better, but this guy ask for HDD, not tapes.
Space limit or cost is the must trade-off for guarantee reliability. Server HDD use more advanced techniques to ensure it from both design and implementation point of view that's why the space is limited and the cost is increased.
2.5-inch disc is better than 3.5-inch from design point of view as it have shorter seeking time (This is obvious as the seeking distance is shorter) and more important, more reliable as less repeatable runout (RRO) will occur (This is not so obvious but think it in this way, RRO is majorly caused by the air-flow caused by disc spinning, smaller disc cause less air-flow, thus less RRO). Generally the smaller is surely better
For electrical-saw-like sound, I don't know where you get this idea, but I can tell you this is completely wrong. I had ever drived one 5400RPM desktop hardisk (or even worse one, I'm not quite sure) to spin on 10000RPM in DSI and I never got this kind of sound. Thus I don't believe a special-designed and tested spindle motor will be worse than that. I guess the sound may comes from the brake -- you may know server HDD usually implement disc brakes to stop disc from spinning when your turning off the machine.
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