s3 upload speed: duplicity vs s3cmd

[Andrei Pozolotin]

1) I use comcast cable internet to access s3;

2) my reference upload speed as measured by
http://www.speakeasy.net/speedtest/
Download Speed: 25486 kbps (3185.8 KB/sec transfer rate)
Upload Speed: 4211 kbps (526.4 KB/sec transfer rate)

3) using s3cmd
http://s3tools.org/s3cmd
I am able to get sustained s3 upload speed close to 500 KB/sec

4) using duplicity

duplicity \
  --volsize $VOLUME_SIZE \
  --s3-use-new-style \
  --verbosity info \
  --asynchronous-upload \
  --include-globbing-filelist $INCLUDE \
  --exclude-globbing-filelist $EXCLUDE \
  $SOURCE $TARGET

I get only about 250 KB/sec

5) I tried various options, volume sizes, etc
still, I get only about 250 KB/sec no matter what;

any suggestions, please?

thank you.

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user1@wks002:~/.duplicity$ duplicity --version
duplicity 0.6.17

user1@wks002:~/.duplicity$ uname -a
Linux wks002 3.0.0-14-generic-pae #23-Ubuntu SMP Mon Nov 21 22:07:10 UTC 2011 i686 i686 i386 GNU/Linux