[Beowulf] Cluster Uplink via Wireless

Jim Lux James.P.Lux at jpl.nasa.gov
Fri Mar 12 17:22:58 EST 2004

At 01:06 PM 3/12/2004 +0100, Michael Arndt wrote:
>Hello *
>has anyone done a wireless technology uplink to a compute cluster
>that is in real use ?
>If so, i would be interested to know how and how is the experinece in
>transferring  "greater" (e.g. 2 GB ++ ) Result files?
>We have a cluster with gigabit interconnect
>where it would make life cheaper, if there is a possibility to upload
>input data and download output data via wireless link, since connecting
>twisted pair between WS and CLuster would be expensive.
I have a very small cluster that is using wireless interconnect for 
everything, and based upon my early observations, I'd be real, real leery 
of contemplating transferring Gigabytes in any practical time. For 
instance, loading a 25 MB compressed ram file system using tftp during PXE 
boot takes about a minute. This is on a very non-optimized configuration 
using 802.11a, through  a variety of devices.

Yes, indeed, the ad literature claims 54 Mbps, but that's not the actual 
data rate, but more the "bit rate" of the over the air signal.  Wireless 
LANs are NOT full duplex, and there are synchronization preambles, etc. 
that make the throughput much lower.

On a standard "11 Mbps" 802.11b type network, the "real data throughput" in 
a unidirectional transfer is probably closer to 3-5 Mbps.

Say you get that wireless link really humming at 20 Mbps real data 
rate.  Transferring 16,000 Mbit is still going to take 10-15 minutes.

Your situation might be a bit better, especially if you can use a point to 
point wireless link.

James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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