disadvantages of a linux cluster

Sam Daniel samhdaniel at earthlink.net
Tue Nov 12 10:47:08 EST 2002


Dr. Wu-chen Feng and others from the Supercomputing in Small Spaces 
group at Los Alamos National Labs presented a paper called "Honey, I 
Shrunk the Beowulf" which provides answers to many of the questions 
being asked here.

The link is:  http://public.lanl.gov/feng/icpp02.pdf

--Sam

Robert G. Brown wrote:
> On Tue, 12 Nov 2002, Guy Coates wrote:
> 
> 
>>>Just for the record, how much did this cluster cost?  Or at least, how
>>>much does a 3U with 24 blades cost?
>>
>>Can't comment on how much we paid I'm afraid, but list price for a 800Mhz
>>PIII blade is $1,249 (you have to figure in the cost of the chassis as
>>well, the price of which does not seem to be on rlx's website).
>>
>>Performance wise, linpack pulls about ~550 Mflops on a single blade.
>>(dmesg reports 1592.52 BogoMIPS per CPU). Disk IO isn't great (ide disks)
>>but there are two of them per blade so we use  RAID-0 which helps. The
>>network is only 100BaseT which is not good if you run MPI (we don't) but
>>there are 3 interfaces per card which allows us to run a slightly strange
>>network topology in order to move large datafiles onto the blades in a
>>sensible amount of time.
> 
> 
> Can one elect to omit one or both disks?  Ethernet interface(s)?  Disks
> and network interfaces can both be passive power consumers and a linux
> image for nodes occupies at most a couple of GB and as little as a few
> tens of MB.  These blades sound like they were born to run diskless in a
> compute farm for EP tasks (where one wouldn't really need multiple
> network interfaces if the task was scaled to run for times much longer
> than startup and data collection), and if one could knock a few hundred
> off the price per blade, would come in at order of $1/MHz, very
> comparable to lintel.
> 
> One does have to worry a bit about getting off the beaten COTS track --
> single source vendor, price to be negotiated with same, single source of
> service -- but Myrinet sets a long precedent and it does sound like a
> nifty cluster;-)
> 
> 
>>>So you don't seem to be getting a lot more MHz/Watt,
>>
>>Probably not too surprising, as the CPU and disks are going to be the
>>major power draw, and they are bog-standard PC parts, same as in every
>>other Lintel cluster.
> 
> 
> Ah, I thought you had the transmeta blade.  Well, that simplifies
> guestimating and comparing P6-family performance and addresses at least
> part of the COTS issue as well:-) One wonders why they can't sell the
> blades with 1.4 GHz PIII's?  They must be using the low voltage/power
> chips, although I find it a bit hard to get full technical specs from
> their website.  Looks like they really want to sell "standard" blades
> without a lot of configuration choices (not unreasonably).
> 
> 
>>The blades are very easy to manage. There are no user-serviceable parts on
>>a blade. So if a disk or CPU dies we pull the whole blade and replace with
>>a new one.  Whether this is a good thing or not depends on how well you
>>get on with your vendor and the T&Cs of your service agreement:). RLX have
>>some nifty blade management software which we use to provision OSs, look
>>at hardware health, get serial consoles etc.
> 
> 
> Do the NICs do PXE?  Can they run diskless?  RLX is clearly selling
> webfarms and server farms with beowulfery an important but secondary
> sales target, but they might consider selling a stripped blade
> engineered as a pure compute node.  It would save a bunch of power, too
> -- disks and unnecessary NICS draw wattage, probably close to half the
> total draw of the boards.  At (say) 500-600W per 3U your power/heat
> problem is fairly significantly reduced, and the lifetime of the boards
> at a lower operating temperature extended.
> 
> BTW, the chassis price from their website was around $3K, making a fully
> populated 24 blade unit with ~$1500 boards about $40K, about $2 per
> aggregate P6 MHz.  A dual Xeon with two 2.4 GHz P4's is about $2000
> (depending on configuration -- probably with a lot more memory) or a bit
> less than $1/MHz (although it also underperforms a PIII relative to
> clock in a some applications, including mine).
> 
> If RLX could find a way of selling stripped, bigger memory but lower
> power compute blades for <$1000 they'd be very cost competitive.  Of
> course, I suppose that this is a matter of dickering with them;-)
> 
> Thanks, this has been very informative.  I was never convinced by the
> "power density" argument the last time blade computers were brought up
> on the list, as the issue isn't power per chip, it is power per MHz and
> given roughly constant switching power requirements at a given VLSI
> scale, one doesn't expect a tremendous difference in power consumption
> between 3 800 MHz P6's and one 2.4 GHz P6.  A fully loaded 40U rack
> (allowing 4U of space at the top for patch panels or switches) can hold
> 12 3U boxes, or 10+ KW of power.  That is, umm, HOT -- a 4 ton A/C with
> massive airflow can just be attached to the front of the rack, thank you
> very much:-)
> 
> I am a lot more likely to be convinced by ease of installation and
> management issues, FLOPS rack densities, and long term reliability.  It
> looks like your cluster does quite well on the first ones, and the last
> one remains to be proven in application.
> 
>   rgb
> 
> 
>>Cheers,
>>
>>Guy Coates
>>
>>
> 
> 


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