[Udpcast] Udpcast lzop and gzip

Alain Knaff alain at knaff.lu
Sat Dec 31 07:06:06 CET 2005


D Teed wrote:
> Be careful comparing the data transfer rate.  That doesn't
> measure how fast you are writing the info to disk, and
> in the end, that is the only thing that matters in
> the performance of udpcast.  Time the job with a clock/watch
> and compare the times.

Indeed. The bandwidth displayed by udpcast is the bandwidth needed to 
transmit the *compressed* data. If you have a very compressible disk, 
the limiting factor now becomes the disk read speed, and compressed 
(network) bandwidth will drop. However, the useful bandwidth 
(uncompressed data), which is not displayed, will rise.

[...]
> At our institution, using gzip, we write 40GB to P4-M notebooks
> in 34 minutes, regardless how much non-zeroed data there is to write
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Normally, if everything works correctly, it should be quicker to 
transmit images which contain lots of zeroed data. However, in such 
case, the *displayed* bandwidth (network bandwidth) will be lower, 
because such data still needs to be read from the disk, and udp-sender 
will end up waiting for the disk, rather than the network.

Regards,

Alain



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