diskless nodes? (was Re: Xbox clusters?)

Carlos O'Donell Jr. carlos at baldric.uwo.ca
Fri Dec 7 06:06:00 PST 2001

> As always YMMV. But quantum chemistry is an application in which the disk
> access can be crucial. I've seen differences in total run time for a job
> of a factor 3 between a disk accesed thru DMA and Non-DMA. If you have to
> do all scratch space over NFS you will even have lower performance.
> Groeten, David.
> ________________________________________________________________________
> Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
> Husargatan 3, Box 576,  	75123 Uppsala, Sweden
> phone:	46 18 471 4205		fax: 46 18 511 755
> spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Have you tested this with NFSv3 on a 100Mbit switched network?
(With enough BW on the backplane of your switch)

Wong, if you are reading this post, you are the only quantum
chemist on Campus with a cluster so you might be able to shed some
more light on the issue ;)

I'd be interested in seeing your results, as the network
may offer better latency than the disk (depends on disk and network

I would assume also that since you are doing local disk writes
that the information is "scratch-pad" in nature?


Just pondering again the issues of latency:

1. Does a poorly written driver and or NIC hardware produce
   that much higher latency? (/me looks at 3C59x based card in box)

2. Does the latency of the disk as a physical device really
   exceed that of a qualitatively _good_ network card on a 100Mbit
   switched topology? (No definition of "good" yet).


I've heard a lot of good and bad things with regards to:

1. Shared network memory use NBD / other technology.
2. Diskless nodes.

And both seem to be a factor of:

Process Related:

a. How much traffic you already have on the network ?
b. Are your local disks fast / always on ?
c. The peak BW you _expect_ out of that tier/level of storage?
d. The sustained BW you would like at any given point?


e. Software Maintenance 
	- Request/Change Cycle
f. Hardware Maintenance 
	- Break/Replace or New-Install cycles

Maybe it's time to do some tests and produce pretty graphs.

Also note that some items in "Administrativa" go away when
you buy from larger companies that have maintenance 
warranties (conceed that you can't know in advance when
things will break).

Carlos O'Donell Jr.
University of Western Ontario
Baldric http://www.baldric.uwo.ca
Admin / Developer / User

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