Transcript http://www.terena.org/activities/nrens-n-grids/workshop-01/leine...

PERT – Beyond Fat Pipes
Simon Leinen <[email protected]>
2005 © SWITCH
Contents
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End-to-end performance initiatives and PERT history
Example PERT activities: GN2-PACE and SWITCH
Lessons learned so far
How Grid developers and users can benefit from PERT
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End-to-End Performance Initiatives
Motivation
• Observation: Backbone improvements not reflected at end users
• Frustrations with differentiated-QoS mechanisms
Ideas for improvement
• Education (close the “wizard gap”)
• Measurement infrastructures
– In the network, e.g. GN2-JRA1
– In the hosts, e.g. Web100
• Human support infrastructure → PERT
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Example PERT Initiatives
GN2 “PACE” (formerly known as “SA3”) PERT
• Oriented towards European projects—including Grids
• Large virtual team with participants from many NRENs
SWITCH PERT
• Includes support for performance of the “commodity” Internet
• Small team from our NOC/network engineering group
Other NRENs are building PERT groups as well
but these two I’m most familiar with…
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DEISAThroughputReduction
Example GN2 PERT Issue
• Iperf (single-stream TCP) measurements between the German and
French DEISA sites usually achieve 900 Mb/s.
• DEISA traffic uses Premium IP inside the GEANT backbone.
• In parallel, there are 2-3 Gb/s throughput tests between Karlsruhe
and CERN, using LBE (Less Than Best Effort) inside GEANT.
• Although there shouldn’t be an impact, DEISA measurements drop
to 400 Mb/s during the Karlsruhe/CERN tests.
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Slow access to download.microsoft.com
Example SWITCH PERT Issue
• Users at site X observe low download speeds from software
distribution site (30-70 kbps)
• First tests from a test host close to X result in good rates (30-40
Mbps) → probably an issue within site X, right?
• However, subsequent tests reproduce rates similar to what the
customer observed.
• Further investigation shows that mapping of
download.microsoft.com to actual hosts is highly variable,
and the performance of the servers mapped to is even more
variable.
• Because SWITCH doesn’t entertain business relationships with
Microsoft of its content distributors, suggested that our customer
complain to Microsoft (of which they are also a customer).
• Although technically a PERT failure, customer seems happy.
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Lessons Learned So Far
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It’s hard to establish contacts with the customer
It’s easy to “lose” the customer
Performance expectations are often unclear
Very hard to close an issue
– Lack of criteria for problem resolution
• Should think in terms of bottlenecks rather than “problem locations”
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How Grid Developers & Users Can Benefit
PERT Knowledgebase (http://kb.pert.switch.ch/)
• Lots of performance-related information
• In the process of being built
• (try to) Use & contribute!
Contact the PERT in case of performance problems
• If it happens when using GEANT/GN2
• After other avenues have been explored (campus system and
networking support)
• Through your NREN or (for groups such as DEISA) directly
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