1U P4 Systems

[Bob Drzyzgula]

On Tue, May 22, 2001 at 05:47:52PM -0400, Robert G. Brown wrote:
> 
> Martin, I'd have to echo this frustration.  Pretty much all the XU cases
> I've found are more than $200, some quite a bit more.  Then you've got
> to buy the rack.  Compared to $50-60 for a standard mid-tower case this
> is painful beyond measure when buying in volume, especially when the
> total node cost might only be $600-750 outside of the case.

Robert,

First, I'll say that I believe that the #1 reason why
rack-mount cases cost this much is that they sell at that
price, in sufficient numbers so as to make a comfortable
profit for the case manufacturers. If everyone would
just stop buying them at that price, we might see some
improvement. :-) Then again, this might just make them
*more* expensive, depending. :-(

This does beg the question of why low-cost competition
does not yet exist. I'd guess that problem is partly in
the sales volumes vs. engineering NRCs. But it may also
partly be in the the mechanicals -- a 2U, rack-mount
chassis needs to have a skin that is much more rigid
than that required for a minitower -- a minitower gets a
lot of its rigidity from the internal framing structure,
which in turn can get its rigidity from being stamped and
bent into weight-efficient but volume-inefficient support
braces and trusses. This is much harder to do in a flat
box like a 2U chassis.

Consider two chassis, a 3.5"x24"x17" rackmount and
a 17"x18"x8" minitower (both height x depth x width).
The rackmount has a volume of 1428 i^3 and a surface area
of 1103 i^2, while the minitower has a volume of 2448 i^3
and a surface area of 1172 i^3. The rackmount's cover
and base, flat surfaces which need to be supported and
kept flat, are 408 i^2, with a 29" diagonal, while the
comparable surfaces in the minitower are 144 i^2 with a
diagonal of 19". The rackmount has a broader expanse of
metal to be kept flat at the same time that it has less
internal space to use up doing it.

It's probably also partly because of the power supply
constraints -- a typical, hyper-mass-produced ATX power
supply is too tall to fit in a 2U chassis, and a 300W power
supply for a 1U chassis will be significantly harder to do;
think about the big electrolytics and transformers which
have to somehow be fit into a space no more than 1.25"
tall (leaving 0.5" for sheet metal and air). I just took
apart a dead 235W Sparkle supply and there's got to be a
dozen components and subassemblies in there that are more
than 1.25" tall; several are more than 2" tall. There's
electrolytics, heat sinks, circuit subassemblies,
transformers and a big old toroid which would all have
to be re-engineered or at least re-mounted horizontally,
sucking up precious board surface area, and that's just
in a 235W supply.

> I regretfully opted for shelves of midtowers for my latest effort(s) --
> one can achieve something like (within a factor of 2, surely) of the
> packing of 2U cases -- I can fairly easily get 16 nodes in a 1-1.5 m^2
> floorspace footprint (depending on how you like to count the gaps
> between units) without going over two nodes high and could double that
> with tall shelves.

This does a good job of fitting the requirements
of an ad-hoc or perhaps a lab environment, but in a
production data center environment these can be decidedly
sub-optimal. It is relatively difficult to get good cooling
for hundreds of devices in a small area in open-frame
racks like this. At my office we have about thirty-five 19"
racks in four rows, bolted side-to-side with panels on the
ends of each row, and doors on the front and backs of each
rack. (This is just for my group -- there are well over
a hundred other racks in this data center.) They sit on a
raised floor with positive plenum pressure into the base
of the rack, fed by recirculating chillers and assisted
by fan trays in the tops and bottoms of the racks. Even
in this environment we run into heat problems when the
system density gets high. (FWIW, what we are short on is
chiller capacity; some of our racks are gulpling for
chilled air.)

> It's not as pretty and it is a bit more work to put together neatly, but
> I still assembled a 16 node cluster in about four hours total work
> including assembling the heavy duty steel shelving.  The shelving itself
> cost only $50 total (plus another $50 or so for cable ties and surge
> protectors and miscellany to make it look nice) saving me about $2500.
> That's serious money for six hours of work (allowing for the time to
> drive to Home Depot and buy the shelving:-) -- 3 nodes worth of money.
> I'll make the time back in the first DAY of fulltime operation.

FWIW, at home I use one of those NSF-certified wire racks,
the kind where you can tie wrap everything to death.
If you have access to a Costco Warehouse store, see if they
have these in stock. At the one near me (Gaithersburg, MD),
they carry a setup with two-section 6' poles, four 18"x48"
shelves with centerline bracing, 5" back fences for each
shelf (great for tie-wrapping cable trunks), locking 4"
hard rubber casters and leveling glides to use if you don't
want to use the casters. These take about ten minutes to
put together if you've done it a few times and know the
tricks. You can easily fit as many as twenty minitowers on
one of these, and wheel it around when you're done. For
this they want $77. Talk about the advantages of volume
production...

http://www.costco.com/frameset.asp?trg=product%2Easp&catid=114&subid=858&hierid=1090&prdid=10002618&log=

> Case vendors take note: there is some insanity here.  Perhaps a 1U case
> is tricky, but a 2U case is pretty nearly a desktop case with rack
> mounts on the side.  In all cases they are basically sheetmetal boxes
> with a motherboard mount, a power supply, and a place to hang a disk and
> a place to poke a card or three out.  No way that 4x is a reasonable
> multiplier for the retail cost -- it just holds down your volume in the
> beowulf and server market.

Not so sure about this. See above.

> I'd like to see 1U or 2U cases selling for a competitive $50-75 (where
> the margin allows for a bit of extra cooling for the 1U cases).

I think that the production volumes would have to go up
dramatically for this to happen, and even then there will
probably always be a significant price premium because most
customers will be businesses, not individual consumers, and
businesses will in fact pay more for something like this.
What the market will bear and all that.

> But I don't think I'm going to anytime soon...:-(

Probably not.

--Bob