Racks vs. pile of PCs

[Marshall E. Fryman]

>Racks better than piles:
>
>1.  Space efficiency.
>2.  Aesthetics (racks look cool)
>
>Piles better than racks (these are not orthogonal):
>
>1.  Internal space constraints

Internal space can be adjusted by getting a bigger case, go from a 1U to a 
2U or even a 4U.

>2.  CPU/motherboard Cooling.  This follows from [1].

Not true. A well designed rack can cool better than a standard PC because 
it is actually forcing better air flow. Most inexpensive PC cases rely more 
on ambient circulation than forcing air to be evacuated from the CPU and 
drive area. The better designed PC cases are going to be more comparable in 
price to the rack mount case and have a similar fan arrangement (or at 
least support for fans, I have an Antec PC server case that has clip-on 
mount points for fans for every 3 drives but no fans were provided.)

>3.  Motherboard/CPU options.  This follows from [1].
>     With a few exceptions most motherboard/CPU combinations
>     will fit into a standard ATX case -  good luck getting
>     a 2.4 Ghz P4 into a 1U.

Check supermicro.com, they have a couple of 1U dual Xeon cases available.

>4.  Initial purchase price for equivalent performance.

Rack mount cases can be more expensive, depends on which rack mount you get 
and which PC case . I recently bought several from buy.com (Antec 2U26 
cases, which I don't really recommend BTW) that were about $270 each. I've 
seen them since for less. The SuperMicro PC server case was $700 (mind you, 
it had hot-swap power supplies and a hot-swap SCSI drive cage.)

>5.  Maintenance costs (rack parts tend to be nonstandard
>     and expensive to replace, for instance, 1U power supplies).

How often do you have to change them? Any good power supply should have a 
MTBF of 50k hours or so. That's about 5.7 years. Even a a 20k is still 2.2 
years.

>Other factors?

The best part about the rack mount's is being able to put the whole cluster 
on something with wheels and then push it wherever you need to go with it. 
Especially nice if you need to get behind the pile to change a cable or you 
have to move them for maintenance of the room or whatever.

>I estimate that for a small cluster (<1 rack's worth of equipment) with
>node guts (mobo,CPU,disk,ram) costing <= $1200 the racked version
>will cost at least 20-30% more than the piled version.  So if a piled
>20 node cluster costs $24000, the equivalent racked version will
>be at least $30000.   $6000 seems a lot to pay for no extra performance.
>If the "guts" were much more expensive the additional rack costs would,
>in theory be a lower percentage.  In practice, it is my impression that
>the ratio is no lower because the vendors charge even more for the
>racked versions of high performance nodes.

prices are from buy.com which is purely retail.

$265 - supermicro SC8221-300LP 2U case
$468 - supermicro P4DPE
$470 - 2x dual xeon 1.8Ghz @ $235
$81   - 40GB IDE HD
$299 - 1GB ECC DDR RAM
--------
$1583

$135 - antec SX1040B PC case (400W PS)
$468 - supermicro P4DPE
$470 - 2x dual xeon 1.8Ghz @ $235
$81   - 40GB IDE HD
$299 - 1GB ECC DDR RAM
--------
$1453

8.9% difference in price

you could also get the Antec 4U case for $173 which would bring the 
difference even closer.

hope it helps.

marshall fryman
futura international, inc.