mini-cluster network delays

Kris Thielemans kris.thielemans at ic.ac.uk
Wed Jan 17 10:51:22 EST 2001


Hi,

we have really funny timings when getting data from one Linux machine to
another. I did the timings with ftp (because that reports them), but I have
the impression the same problems exist when doing regular cp etc. Also,
because I use ftp, I think I minimise NIS access (I don't need to check
mount points etc.)
Hi,

I have some delays in network access between different machines in our
mini-cluster. This is not really a beowulf (yet), but I hope somebody can
help me how to find out what's going wrong.

Our cluster has 4 identical Linux PCs (SuSE 6.3), each of them with  100Mbit
Ethernet connection to an Ethernet switch (and from the switch also a 10Mbit
to the 'outside').


We have really funny timings when getting data from one Linux machine to
another. I did the timings with ftp (because that reports them), but I have
the impression the same problems exist when doing regular cp etc. Also,
because I use ftp, I think I minimise NIS access (I don't need to check
mount points etc.)

So I'm ftp-ing a file of 5.7 MB (binary mode). Below is are some examples of
timings of ftp-ing this file between the different machines (called pp1-pp4)

from	to	time (secs)
pp2	pp1	6.5
pp1	pp2	20
pp1	pp3	1.5
pp3	pp1	1.5
pp3	pp2	21
pp2	pp3	6.5
pp1	pp4	21
pp4	pp1	6.5
pp2	pp4	7
pp4	pp2	6.5
pp3	pp4	21.5

as comparison:
pp3	pp3		0.14 (from 1 machine to itself)
pp1	outside	17.5 (depends on network traffic heavily)
outside pp1		7.5

Obviously we want to have the performance of pp1<->pp3 everywhere.

Any ideas where this can come from or how to find out what causes this?

Thanks
Kris

PS:
(One fairly nasty thing is that users and groups are defined on a NIS server
which is 'outside'. We want to rememdy this in the future, but had some
problems having a local NIS server on one machine, which would still know
about the outside NIS server. Anyway. I hope this i snot important right
now.)

Kris Thielemans
MRC Cyclotron Unit,
Hammersmith Hospital,
DuCane Rd,London W12 0NN, United Kingdom

NEW web site address:
http://www.cu.mrc.ac.uk/~kris



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