Speaker
Christopher John Walker
(University of London (GB))
Description
The WLCG, and high energy physics in general, relies on remote Tier-2
sites to analyse the large quantities of data produced. Transferring
this data in a timely manner requires significant tuning to make
optimum usage of expensive WAN links.
In this paper we describe the techniques we have used at QMUL to
optimise network transfers. Use of the FTS with settings and
appropriate TCP window sizes allowed us to saturate a 1 Gbit link for
24 hours - whilst still achieving acceptable download speeds. Source
based routing and multiple gridftp servers allowed us to use an
otherwise unused "resilient" link.
After the WAN link was upgraded to 10Gbit/s, a significant reduction
in transfer rates was observed from some sites - due to suboptimal
routing resulting in packet loss on congested links. Solving this
dramatically improved performance.
The use of jumbo frames (MTU=9000) offers potential improvements in
performance, particularly for latency limited links. Whilst much of
the Internet backbone is capable of supporting this, most sites are
not, and path MTU discovery fails at some sites. We describe our
experience with this.
Author
Christopher John Walker
(University of London (GB))
Co-authors
Daniel Peter Traynor
(University of London (GB))
Duncan Rand
(Imperial College)
Steve Lloyd
(University of London (GB))
