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emulab.net: An Emulation Testbed for Networks and Distributed Systems. Jay Lepreau and many others University of Utah Intel IXA University Workshop June 21, 2001. The Main Players. Undergrads Chris Alfeld, Chad Barb, Rob Ricci Grads - PowerPoint PPT Presentation
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emulab.net:An Emulation Testbed for Networks and Distributed
Systems
Jay Lepreau
and
many others
University of Utah
Intel IXA University Workshop
June 21, 2001
The Main Players Undergrads
– Chris Alfeld, Chad Barb, Rob Ricci
Grads– Dave Andersen, Shashi Guruprasad, Abhijeet
Joglekar, Indrajeet Kumar, Mac Newbold Staff
– Mike Hibler, Leigh Stoller
Alumni– Various
(Red: here at Intel today)
What?
A configurable Internet emulator in a room– Today: 200 nodes, 500 wires, 2x BFS (switch)– virtualizable topology, links, software
Bare hardware with lots of tools An instrument for experimental CS research Universally available to any remote
experimenter Simple to use
What’s a Node?
Physical hardware: PCs, StrongARMs
Virtual node:– Router (network emulation)– Host, middlebox (distributed system)
Future physical hardware: IXP1200 +
Why?
“We evaluated our system on five nodes.” -job talk from university with 300-node cluster
“We evaluated our Web proxy design with 10 clients on 100Mbit ethernet.”
“Simulation results indicate ...” “Memory and CPU demands on the individual
nodes were not measured, but we believe will be modest.”
“The authors ignore interrupt handling overhead in their evaluation, which likely dominates all other costs.”
“Resource control remains an open problem.”
Why 2
“You have to know the right people to get access to the cluster.”
“The cluster is hard to use.” “<Experimental network X> runs FreeBSD
2.2.x.” “October’s schedule for <experimental
network Y> is…” “<Experimental network Z> is tunneled
through the Internet”
Complementary to Other Experimental Environments
Simulation Small static testbeds Live networks Maybe someday, a large scale set of
distributed small testbeds (“Access”)
Switched “Backplane”
PCPC
Web/DB/SNMPSwitch MgmtUsers
Internet
Control Switch/Router
Serial
Sharks Sharks
16040
PowerCntl
Zoom In: One Node
Fundamental Leverage:
Extremely ConfigurableEasy to Use
Key Design Aspects
Allow experimenter complete control … but provide fast tools for common
cases– OS’s, disk loading, state mgmt tools, IP, traffic
generation, batch, ...
Virtualization– of all experimenter-visible resources– node names, network interface names,
network addresses– Allows swapin/swapout
Design Aspects (cont’d)
Flexible, extensible, powerful allocation algorithm
Persistent state maintenance:– none on nodes– all in database– leverage node boot time: only known state!
Separate control network Familiar, powerful, extensible
configuration language: ns
Some Unique Characteristics
User-configurable control of “physical” characteristics: shaping of link latency/bandwidth/drops/errors(via invisibly interposed “shaping nodes”), router processing power, buffer space, …
Node breakdown today:– 40 core, 160 edge
More Unique Characteristics
Capture of low-level node behavior such as interrupt load and memory bandwidth
User-replaceable node OS softwareUser-configurable physical link
topologyCompletely configurable and usable
by external researchers, including node power cycling
Obligatory Pictures
Then
Now
A Few Research Issues and Challenges
Network management of unknown entities
Security Scheduling of experiments Calibration, validation, and scaling Artifact detection and control NP-hard virtual --> physical mapping
problem Providing a reasonable user interface ….
An “Experiment”
emulab’s central operational entity Directly generated by an ns script, … then represented entirely by
database state
Steps: Web, compile ns script, map, allocate, provide access, assign IP addrs, host names, configure VLANs, load disks, reboot, configure OS’s, run, report
Mapping Example
Automatic mapping of desired topologies and
characteristics to physical resources
Algorithm goals:– minimize likelihood of experimental artifacts (bottlenecks)– “optimal” packing of multiple simultaneous experiments– Extensible for heterogenous hardware, software, new
features
Randomized heuristic algorithm: simulated annealing
May move to genetic algorithm
Virtual Topology
Mapping into Physical Topology
Mapping Results
< 1 second for first solution, 40 nodes
“Good” solution within 5 secondsApparently insensitive to number
of node “features”
Disk Loading
13 GB generic IDE 7200 rpm drivesWas 20 minutes for 6 GB imageNow 88 seconds
How?
Do obvious compression… and a little less obvious: zero
the fsDisk writes become the bottleneckHack the disk driverCarefully overlap I/O and
decompression==> 6 minutes
Last Step
Domain-specific compressionType the filesystem blocks:
– allocated– free
Never write the free ones
Experiment Creation Time
Experiment Termination Time
Ongoing and Future Work
Multicast disk images IXP1200 nodes, tools, code fragments
– Routers, high-capacity shapers
Event system Scheduling system Topology generation tools and GUI Simulation/enulation transparency Linked testbeds Wireless nodes, Mobile nodes Logging. Visualization tools Microsoft OSs, high speed links, more nodes!
Final Remarks
18 projects have used it (14 external)– Plus several class projects
Two OSDI’00 and three SOSP’01 papers– 20% SOSP general acceptance rate– 60% SOSP acceptance rate for emulab users!
More emulab’s under construction:– Yes: Univ. of Kentucky, Stuttgart– Maybe: WUSTL, Duke
Sponsors (red: major ones, current or expected)– NSF, DARPA, University of Utah– Cisco, Intel, Compaq, Microsoft, Novell, Nortel
Available for universities, labs, and
companies at:
www.emulab.net