1 High Performance WAN Testbed Experiences & Results Les Cottrell – SLAC Prepared for the CHEP03, San Diego, March Partially funded by DOE/MICS Field Work Proposal on Internet End-to-end Performance Monitoring (IEPM), by the SciDAC base program.

2 Outline Who did it? What was done? How was it done? Who needs it? So what’s next? Where do I find out more?

3 Who did it: Collaborators and sponsors Caltech: Harvey Newman, Steven Low, Sylvain Ravot, Cheng Jin, Xiaoling Wei, Suresh Singh, Julian Bunn SLAC: Les Cottrell, Gary Buhrmaster, Fabrizio Coccetti LANL: Wu-chun Feng, Eric Weigle, Gus Hurwitz, Adam Englehart NIKHEF/UvA: Cees DeLaat, Antony Antony CERN: Olivier Martin, Paolo Moroni ANL: Linda Winkler DataTAG, StarLight, TeraGrid, SURFnet, NetherLight, Deutsche Telecom, Information Society Technologies Cisco, Level(3), Intel DoE, European Commission, NSF

4 What was done? Beat the Gbps limit for a single TCP stream across the Atlantic – transferred a TByte in an hour WhenFromToBottle- neck MTUStrea ms TCPThru- put Nov ’02 (SC02) Amste rdam Sunny- vale 1 Gbps9000B1Stand ard 923 Mbps Nov ’02 (SC02) Balti- more Sunny- vale 10 Gbps FAST8.6 Gbps Feb ‘03Sunny -vale Geneva2.5 Gbps 9000B1Stand ard 2.38 Gbps Set a new Internet2 TCP land speed record, 10,619 Tbit-meters/sec –(see With 10 streams achieved 8.6Gbps across US One Terabyte transferred in less than one hour

5 On February 27-28, over a Terabyte of data was transferred in 3700 seconds by S. Ravot of Caltech between the Level3 PoP in Sunnyvale, near SLAC, and CERN. The data passed through the TeraGrid router at StarLight from memory to memory as a single TCP/IP stream at an average rate of 2.38 Gbps (using large windows and 9KByte “jumbo” frames). This beat the former record by a factor of approximately 2.5, and used the US-CERN link at 99% efficiency. 10GigE Data Transfer Trial European Commission Original slide by: Olivier Martin, CERN

6 How was it done: Typical testbed 12*2cpu servers 4 disk servers GSRGSR 6*2cpu servers Sunnyvale 6*2cpu servers 4 disk servers OC192/POS (10Gbits/s) 2.5Gbits/s T640T640 Sunnyvale section deployed for SC2002 (Nov 02) (EU+US) Geneva Chicago SNV CHIAMS GVA > 10,000 km

7 Typical Components CPU –Pentium 4 (Xeon) with 2.4GHz cpu For GE used Syskonnect NIC For 10GE used Intel NIC –Linux or 20 Routers –Cisco GSR with OC192/POS & 1 and 10GE server interfaces (loaned, list > $1M) –Cisco 760x –Juniper T640 (Chicago) Level(3) OC192/POS fibers (loaned SNV-CHI monthly lease cost ~ $220K) Note bootees Earthquake strap GSR Heat sink Disk servers Compute servers

8 Challenges After a loss it can take over an hour for stock TCP (Reno) to recover to maximum throughput at 1Gbits/s –i.e. loss rate of 1 in ~ 2 Gpkts (3Tbits), or BER of 1 in 3.6*10 12 PCI bus limitations (66MHz * 64 bit = 4.2Gbits/s at best) At 2.5Gbits/s and 180msec RTT requires 120MByte window Some tools (e.g. bbcp) will not allow a large enough window – (bbcp limited to 2MBytes) Slow start problem at 1Gbits/s takes about 5-6 secs for 180msec link, –i.e. if want 90% of measurement in stable (non slow start), need to measure for 60 secs –need to ship >700MBytes at 1Gbits/s Sunnyvale-Geneva, 1500Byte MTU, stock TCP

9 Windows and Streams Well accepted that multiple streams (n) and/or big windows are important to achieve optimal throughput Effectively reduces impact of a loss by 1/n, and improves recovery time by 1/n Optimum windows & streams changes with changes (e.g. utilization) in path, hard to optimize n Can be unfriendly to others

10 Even with big windows (1MB) still need multiple streams with Standard TCP Above knee performance still improves slowly, maybe due to squeezing out others and taking more than fair share due to large number of streams Streams, windows can change during day, hard to optimize ANL, Caltech & RAL reach a knee (between 2 and 24 streams) above this gain in throughput slow

11 New TCP Stacks Reno (AIMD) based, loss indicates congestion –Back off less when see congestion –Recover more quickly after backing off Scalable TCP: exponential recovery –Tom Kelly, Scalable TCP: Improving Performance in Highspeed Wide Area Networks Submitted for publication, December High Speed TCP: same as Reno for low performance, then increase window more & more aggressively as window increases using a table Vegas based, RTT indicates congestion –Caltech FAST TCP, quicker response to congestion, but … Standard Scalable High Speed

12 Stock vs FAST TCP MTU=1500B Need to measure all parameters to understand effects of parameters, configurations: –Windows, streams, txqueuelen, TCP stack, MTU, NIC card –Lot of variables Examples of 2 TCP stacks –FAST TCP no longer needs multiple streams, this is a major simplification (reduces # variables to tune by 1) Stock TCP, 1500B MTU 65ms RTT FAST TCP, 1500B MTU 65ms RTT FAST TCP, 1500B MTU 65ms RTT

13 Jumbo frames Become more important at higher speeds: –Reduce interrupts to CPU and packets to process, reduce cpu utilization –Similar effect to using multiple streams (T. Hacker) Jumbo can achieve >95% utilization SNV to CHI or GVA with 1 or multiple stream up to Gbit/s Factor 5 improvement over single stream 1500B MTU throughput for stock TCP (SNV-CHI(65ms) & CHI-AMS(128ms)) Complementary approach to a new stack Deployment doubtful –Few sites have deployed –Not part of GE or 10GE standards Jumbos 1500B

14 TCP stacks with 1500B txqueuelen

15 Jumbo frames, new TCP stacks at 1 Gbits/s SNV-GVA

16 Other gotchas Large windows and large number of streams can cause last stream to take a long time to close. Linux memory leak Linux TCP configuration caching What is the window size actually used/reported 32 bit counters in iperf and routers wrap, need latest releases with 64bit counters Effects of txqueuelen (number of packets queued for NIC) Routers do not pass jumbos Performance differs between drivers and NICs from different manufacturers –May require tuning a lot of parameters

17 Who needs it? HENP – current driver Data intensive science: –Astrophysics, Global weather, Fusion, sesimology Industries such as aerospace, medicine, security … Future: –Media distribution Gbits/s=2 full length DVD movies/minute 2.36Gbits/s is equivalent to –Transferring a full CD in 2.3 seconds (i.e CDs/hour) –Transferring 200 full length DVD movies in one hour (i.e. 1 DVD in 18 seconds) Will sharing movies be like sharing music today?

18 What’s next? Break 2.5Gbits/s limit Disk-to-disk throughput & useful applications –Need faster cpus (extra 60% MHz/Mbits/s over TCP for disk to disk), understand how to use multi-processors Evaluate new stacks with real-world links, and other equipment –Other NICs –Response to congestion, pathologies –Fairnesss –Deploy for some major (e.g. HENP/Grid) customer applications Understand how to make 10GE NICs work well with 1500B MTUs

19 More Information Internet2 Land Speed Record Publicity –www-iepm.slac.stanford.edu/lsr/www-iepm.slac.stanford.edu/lsr/ –www-iepm.slac.stanford.edu/lsr2/www-iepm.slac.stanford.edu/lsr2/ 10GE tests –www-iepm.slac.stanford.edu/monitoring/bulk/10ge/www-iepm.slac.stanford.edu/monitoring/bulk/10ge/ –sravot.home.cern.ch/sravot/Networking/10GbE/10GbE_test.htmlsravot.home.cern.ch/sravot/Networking/10GbE/10GbE_test.html TCP stacks –netlab.caltech.edu/FAST/netlab.caltech.edu/FAST/ –datatag.web.cern.ch/datatag/pfldnet2003/papers/kelly.pdfdatatag.web.cern.ch/datatag/pfldnet2003/papers/kelly.pdf – Stack comparisons –www-iepm.slac.stanford.edu/monitoring/bulk/fast/www-iepm.slac.stanford.edu/monitoring/bulk/fast/ –

20 Impact on others