Bill Broadley wrote:
The lid screws down to apply pressure to a piece of foam. Foam presses down on 45 drives. 5 drives (1.4 lb each) sit on each port multipliers. 6 nylon mounts support each multiplier supporting 7 pounds of drives. Seems like the damping from the nylon mounts would be minimal under that much pressure. So on the bottom of the case you have 63 pounds of drives, a significant fraction of which is rotating mass.
... Which is being driven at multiple points by a 120Hz signal (7200RPM). It seems like a basic physics calculation to get the resulting eigen-modes and eigen-frequencies. Looking at the design, I was concerned about the nylon standoffs (high frequency coupling, including octaves of 120Hz) coupling enough vibration into the units.
I wonder if the port multipliers are really designed to actually support the drives. Doesn't seem like the SATA power/data connects I've seen are designed for that.
Technically, they should not be used for structural support. For supporting cables? Sure.
Not to mention it's hard to imagine the typical flexible thin sheet metal lid applying even pressure to 45 drives through the foam. Seems like most of the pressure would be on the drives on the outside edge, leaving the inside drives relatively undamped. My experience is that nylon mounts don't help much. Sure poor manufacturing tolerances, and near zero load/tension often prevent things like fans from tightly coupling with a chassis. But to decouple drive vibration from a chassis seems to require something much more aggressive. Something like a very soft/gooey rubber with a fair bit of travel and give under minimal pressure (4-6 ounces).
Yeah. Looking at this unit, the big issue looks to be vibration. In which case, you probably want better (more vibration tolerant) drives than the ones spec'ed. And a better mounting design.
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