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Infiniband in the Data
Center
Steven Carter
Cisco Systems
stevenca@cisco.com
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
Makia Minich, Nageswara Rao
Oak Ridge National Laboratory
{minich,rao}@ornl.gov
1
Agenda
 Overview
 The Good, The Bad, and The Ugly
 IB LAN Case Study: Oak Ridge National Laboratory
Center for Computational Sciences
 IB WAN Case Study: Department of Energy’s
UltraScience Network
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
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Overview
 Data movement requirements are exploding in HPC
data centers.
 The requirement to move 100’s of GB/s around the data
center requires something more than is being provided
in the Ethernet community
 TCP/IP performs poorly in the wide-area on the highbandwidth links required to move data between data
centers
 This is a high-level overview of the pros and cons of
using Infiniband in the Data Center and two case
studies to reinforce them
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
3
Agenda
 Overview
 The Good, The Bad, and The Ugly
 IB LAN Case Study: Oak Ridge National Laboratory
Center for Computational Sciences
 IB WAN Case Study: Department of Energy’s
UltraScience Network
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
4
The Good
 Cool Name (Marketing gets an A+ -- who doesn’t want
infinite bandwidth?)
 Unified Fabric/IO Virtualization:
– Low-latency interconnect - nanoseconds, not low
milliseconds - not necessarily important in a data center
– Storage – Using SRP (SCSI RDMA Protocol) or iSER (iSCSI
Extension for RDMA)
– IP – Using IPoIB, newer versions run over Connected Mode
giving better throughput
– Gateways – Gateways give access to legacy Ethernet
(careful) and Fibre Channel networks
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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The Good (Cont.)
 Faster link speeds:
– 1x Single Data Rate (SDR) = 2.5 Gb/s (2 Gb/s with 8b/10b
signalling)
– 4 1x links can be aggregated into a single 4x link
– 3 4x links can be aggregated into a single 12x link (single 12x
link also available)
– Double Data Rate (DDR) currently available, Octo Data Rate
(ODR) on the horizon
– Many link speeds available: 8Gb/s, 16Gb/s, 24 Gb/s, 32Gb/s,
48 Gb/s, etc.
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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The Good (Cont.)
 HCA does much of the heavy lifting:
– Much of the protocol is done on the Host Channel Adapter
(HCA) freeing the CPU
– Remote Direct Memory Access (RDMA) gives the ability to
transfer data between hosts with very little CPU overhead
– RDMA capability is EXTREMELY important because it
provides significantly greater capability from the same hardware
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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The Good (Cont.)
 Nearly 10x less cost for similar bandwidth:
– Because of its simplicity, IB switches cost less. Oddly
enough, IB HCAs are more complex than 10G NICs, but are
also less expensive.
– Roughly $500 per port in the switch and $500 for a dual port
DDR HCA
– Because of RDMA, there is a cost savings in infrastructure as
well (i.e. you can do more with fewer hosts)
 Higher port density switches:
– Switches available with 288 (or more) full-rate ports in a single
chassis
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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The Bad
 IB sounds too much like IP (Can quickly degrade into a “Who’s on
first” routine)
 IB is not well understood by networking folks
 Lacks some of the features of Ethernet important in the Data
Center:
– Router – no way to natively connect two separate fabrics - The IB
Subnet Manager (SM) is integral to the operation of the network
(detects hosts, programs routes into the switch, etc). Without a router,
you cannot have two different SMs for different operational or
administrative domains (Can be worked around at the application
layer).
– Firewall – No way to dictate who talks to whom by protocol (partitions
exist, but are too course grained)
– Protocol Analyzers - They exist but are hard to come by, difficult to
“roll your own” because of the protocol is embedded in the HCA
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
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The Ugly
 Cabling options:
•Heavy gage cables with clunky CX4 connectors
•Short distance (< 20 meters)
•If mishandled, they have a propensity to fail
•Heavy connectors can become disengaged
•Electrical to optical converter
•Long distance (up to 150 meters)
•Uses multi-core ribbon fiber (hard to debug)
•Expensive
•Heavy connectors can become disengaged
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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The Ugly (Continued)
 Cabling options:
•Electrical to optical converter built on the cable
•Long distance (up to 100 meters)
•Uses multi-core ribbon fiber (hard to debug)
•More cost effective than other solutions
•Heavy connectors can become disengaged
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
11
Agenda
 Overview
 The Good, The Bad, and The Ugly
 IB LAN Case Study: Oak Ridge National Laboratory
Center for Computational Sciences
 IB WAN Case Study: Department of Energy’s
UltraScience Network
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
12
Case Study: ORNL Center for
Computational Sciences (CCS)
 The Department of Energy established the Leadership
Computing Facility at ORNL’s Center for Computational
Sciences to field a 1PF supercomputer
 The design chosen, the Cray XT series, includes an internal
Lustre filesystem capable of sustaining reads and writes of
240GB/s
 The problem with making the filesystem part of the machine
is that it limits the flexibly of the Lustre filesystem and
increases the complexity of the Cray
 The problem with decoupling the filesystem from the
machine is the high cost involved with to connect it via 10GE
at the required speeds
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
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13
CCS IB Network Roadmap Summary
Ethernet core scaled
to match wide-area
connectivity and
archive
Lustre
Infiniband core scaled to
match central file system
and data transfer
Baker
Gateway
Ethernet
[O(10GB/s)]
Jaguar
Infiniband
[O(100GB/s)]
High-Performance
Storage System
(HPSS)
Viz
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
14
XT3 LAN Testing
Voltaire 9024
Spider
(Linux Cluster)
Rizzo (XT3)
• ORNL showed the first successful
infiniband implementation on the
XT3
• Using Infiniband in the XT3’s I/O
nodes running a Lustre Router
resulted in a > 50% improvement in
performance and a significant
decrease in CPU utilization
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
15
Observations
 XT3's performance is good (better than 10GE) for
RDMA
 XT3's poor performance compared to the generic
X86_64 host likely a result of PCI-X HCA (known to be
sub-optimal)
 In its role as a Lustre router, IB allows significantly
better performance per I/O node allowing CCS to
achieve the required throughput with fewer nodes than
would be needed using 10GE
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
16
Agenda
 Overview
 The Good, The Bad, and The Ugly
 IB LAN Case Study: Oak Ridge National Laboratory
Center for Computational Sciences
 IB WAN Case Study: Department of Energy’s
UltraScience Network
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
17
IB over WAN testing
 Placed 2 x Obsidian Longbow
devices between Voltaire 9024 and
Voltaire 9288
Ciena
CD-CI
(SNV)
DOE
UltraScience
Network
Obsidian
Longbow
Obsidian
Longbow
Ciena
CD-CI
(ORNL)
Voltaire
9024
20
 Provisioned loopback circuits of
various lengths on the DOE
UltraScience Network and ran test.
 RDMA Test Results:
Local: 7.5Gbps (Longbow to Longbow)
ORNL <-> ORNL (0.2mile): 7.5Gbps
ORNL <-> Chicago (1400miles): 7.46Gbps
ORNL <-> Seattle (6600 miles): 7.23Gbps
ORNL <-> Sunnyvale (8600 miles): 7.2Gbps
Voltaire
9288
4x Infiniband SDR
81
OC-192 SONET
Cluster
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
End-to-End
Cisco Public
18
Sunnyvale loopback (8600 miles) –
RC problem
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
19
Observations
 The Obsidian Longbows appear to be extending sufficient link-level
credits
 Native IB transports does not appear to suffer from the same widearea shortcomings as TCP (i.e. Full rate with no tuning)
 With the Arbel based HCAs, we saw problems:
– RC only performs well at large messages sizes
– There seems to be a maximum number of messages allowed in flight
(~250)
– RC performance does not increase rapidly enough even when
message cap is not an issue
 The problems seem to be fixed with the new Hermon-based
HCAs…
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
20
Obsidian’s Results – Arbel vs. Hermon
Arbel to Hermon
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Hermon to Arbel
Cisco Public
21
Summary
 Infiniband has the potential to make a great data center
interconnect because it provides a unified fabric, faster
link speeds, mature RDMA implementation, and lower
cost
 There does not appear to be the same intrinsic problem
with IB in the wide-area as there is with IP/Ethernet,
making IB a good candidate to transfer data between
data centers
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
22
The End
Questions? Comments? Criticisms?
For more information:
Steven Carter
Cisco Systems
stevenca@cisco.com
Infiniband in the
Data Center
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
Makia Minich, Nageswara Rao
Oak Ridge National Laboratory
{minich,rao}@ornl.gov
23