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SEDCL: Stanford Experimental Data Center Laboratory . Tackle Data Center Scaling Challenges with Stanford’s research depth and breadth. Data Center Scaling. A network of data centers and web services are the key building blocks for future computing

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tackle data center scaling challenges with stanford s research depth and breadth

Tackle Data Center Scaling Challenges with Stanford’s research depth and breadth

data center scaling
Data Center Scaling
  • A network of data centers and web services are the key building blocks for future computing
  • Factors contributing to data center scaling challenges
    • Explosive growth of data with no locality of any kind
    • Legal requirement to backup data in geographically-separated locations---big concern for financial industry
    • Emergence of mobile and Cloud Computing
    • Massive “interactive” web application
    • Energy as a major new factor and constraint
    • Increasing capex and opex pressures
  • Continued innovations critical to sustain growth
stanford research themes
Stanford Research Themes
  • RAMCloud: main-memory based persistent storage
    • Extremely low latency RPC
  • Networking:
    • Large, high-bandwidth, low-latency network fabric
    • Scalable, error-free packet transport
    • Software defined data center networking with OpenFlow
  • Servers and computing
    • Error and failure resilient design
    • Energy aware and energy proportional design
    • Virtualization and mobile VMs
major research topics of sedcl
Major research topics of SEDCL
  • RAMCloud: Scalable DRAM-based Storage
    • Scalable nvRAM
    • All data in DRAMs all the time
  • Interconnect fabric
    • Bufferless networks: low-latency, high-bandwidth network
  • Packet transport
    • Reliable delivery of packets: R2D2—L2.5
    • Congestion management: QCN (IEEE 802.1Qau), ECN-HAT, DCTCP
    • Programmable bandwidth partitioning for multi-tenanted DCs: AF-QCN
    • Low-latency 10GBaseT
  • Related projects
    • OpenFlow
    • Energy aware and energy proportional design
experimentation is key to success
Experimentation is Key to Success
  • Many promising ideas and technologies
    • Will need iterative evaluation at scale with real applications
  • Interactions of subsystems and mechanisms not clear
    • Experimentation best way to understand the interactions
  • Difficult to experiment with internal mechanisms of a DC
    • No experimental facilities and that is a big barrier to innovations
  • Ongoing efforts to enable experimentation
    • Facebook, Microsoft, NEC, Yahoo!, Google, Cisco, Intel, …
overview of research projects
Overview of Research Projects
  • RAMCloud
  • Packet transport mechanisms
    • Reliable and reliable data delivery: R2D2—L2.5
    • ECN-HAT, DCTCP: collaboration with Microsoft
  • Data center switching fabric
    • Extremely low latency, low errors and congestion (bufferless)
    • High port density with very large bisection bandwidth

 project just initiated

ramcloud overview lead john ousterhout
RAMCloud OverviewLead: John Ousterhout

Application Servers

  • Storage for datacenters
  • 1000-10000 commodity servers
  • 64 GB DRAM/server
  • All data always in RAM
  • Durable and available
  • Low-latency access:5µs RPC
  • High throughput:1M ops/sec/server

Storage Servers


ramcloud research issues
RAMCloud Research Issues
  • Data durability and availability
  • Low latency RPC: 5 microseconds
    • Need suitable network!
  • Data model
  • Concurrency/consistency model
  • Data distribution, scaling
  • Automated management
  • Multi-tenancy
  • Client-server functional distribution
layer 2 5 motivation and use cases
Layer 2.5: Motivation and use cases
  • Speed up TCP performance in data centers
    • TCP performs poorly when there is a large number of packet drops
    • Applications like MapReduce/Hadoop and GFS cause the “incast problem” where a large number of packets are dropped at switches
    • L2.5 is a highly scalable method of rapidly retransmitting dropped packets
  • FCoE
    • Corruption losses, though rare, lead to SCSI timeouts.
    • Priority flow control (IEEE 802.1Qbb) enables Ethernet switches not to drop packets, but requires “skid” or “PAUSE-absorption” buffers. But skid buffers grow as bandwidth-delay product of links and are very expensive.
    • L2.5 enables FCoE to overcome corruption losses
l2 5 research issues
L2.5 Research Issues
  • Determine simple signaling method
    • Simplify (or get rid of) headers/tags for L2.5 encapsulation
  • Develop and refine the basic algorithm for TCP
    • In the kernel
    • In hardware (NICs)
  • Develop the algorithm for storage (FC, FCoE)
  • Deploy in a large testbed
  • Collaborate on standardization
  • DCTCP: TCP for data centers
    • Operates with really small buffers
    • Optimized for low-latency
    • Uses ECN marking

 with Mohammad Alizadeh, and Greenberg et al at Microsoft

 Influenced by ECN-HAT (with Abdul Kabbani)

dctcp transport optimized for data centers
DCTCP: Transport Optimized for Data Centers





  • High throughput
    • Creating multi-bit feedback at TCP sources
  • Low Latency (milliseconds matter)
    • Small buffer occupancies due to early and aggressive ECN marking
  • Burst tolerance
    • Sources react before packets are dropped
    • Large buffer headroom for bursts

Packet buffer





Use full info in stream of ECN marks

Adapt quickly and in proportion to level of congestion


Reduces variability

Reduces queuing

research themes and teams
Research Themes and Teams

WEB App Framework

J. Ousterhout

M. Rosenblum

S. Mitra

Resilient Systems

N. McKeown


Server and network

M. Rosenblum

B. Prabhakar

K. Kozyrakis

Energy Aware

P. Levis

N. McKeown

J. Ousterhout


M. RosenblumD. Mazieres

N. McKeown


G. Parulkar

B. Prabhakar