[Beowulf] network transfer issue to disk, old versus new hardware

Bogdan Costescu Bogdan.Costescu at iwr.uni-heidelberg.de
Mon Jun 4 08:07:36 EDT 2007


On Sat, 2 Jun 2007, David Mathog wrote:

> I can't quite wrap my head around a recent nettee result, perhaps
> one of the network gurus here can explain it.

IMHO, it's not a network issue, as is shown by your G results.

>    sync; accudate; dd if=/dev/zero bs=512 count=1000000 of=test.dat;

All your tests use bs=512 - why ? This makes unnecessary trips to 
kernel code and back which result in an increased number of context 
switches and significant slowdown. My guess is that this (high number 
of context switches) plus a high interrupt rate (disk and network 
simultaneously) is the reason for your results.

> Old:  Athlon MP 2200+, Tyan S2466MPX mobo, 2.6.19.3 kernel, 512Mb RAM

I used to have the exact same hardware as cluster nodes (but with dual 
CPU, whether you also have duals is not clear from your post) and 
tried to convert 2 of them to small file-servers - same problem of 
disk + network simultaneous activity. After benchmarking, I gave up - 
this was almost 2 years ago and I don't have the exact numbers 
anymore, but a single PIV 3GHz on a consumer-grade mainboard was able 
to provide significantly better performance for the same task.

--
Bogdan Costescu

IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen
Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY
Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868
E-mail: Bogdan.Costescu at IWR.Uni-Heidelberg.De
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