[Beowulf] petabyte for $117k
landman at scalableinformatics.com
Wed Sep 2 04:28:24 PDT 2009
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.
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman at scalableinformatics.com
web : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
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