TM

Clustering and Networking on LinuxClustering and Networking on Linux

Kumaran KalyanasundaramSGI Technology Center

TMAgenda

• Types of clusters– Examples – Important technologies– Available products

• Cluster interconnects– Speeds and feeds

• Compute clusters– Hardware layouts– Programming considerations

TMTypes of ClustersFunctional View

Availability clusters: For “mission-critical” apps– RAS features are essential requirements for all clusters

Throughput clusters: Run multiple jobs on nodes in the cluster

– Mostly batch-style apps that are not “cluster-aware”– Scheduling, load-balancing

Capability clusters: Run a cluster-aware (HPC/MPI) job on multiple nodes

TMClustering for High Availability

A collection of systems in a cluster, lends itself well to providing significantly higher availability when compared to a standalone system. – If one fails, move to the other!

Significantly higher availability with moderate cost overhead– all systems actively engaged in the cluster workload

TMWhat is High Availability?

• When System or service are available almost all the time!• Resiliency from any single point of failure• Availability at or above 99.9%

– accumulated unplanned outages less than 8 hrs / year

• Minimized Downtime, services made available much before the broken component gets fixed.

• Can hide planned downtime as well

TMThe High-Availability Environment

• Member nodes of the HA cluster

• Services/applications to be made highly available

• Resources they depend upon

• Primary node for each of these applications

• Designated alternate node(s) in case of a failure on primary node

TMElements of HA Infrastructure(HW)

Heartbeat

Public Network (Ethernet, FDDI, ATM)

Replicated Data configuration

A B

ServerA

ServerB

changes

TMElements of HA Infrastructure(HW)

ServerA

ServerB

Heartbeat

Reset

Public Network (Ethernet, FDDI, ATM)

Fibre RAID - Dual Hosted storage configuration

A BFibre Loop A Loop B

Controller BController A

TMElements of HA Infrastructure(SW)

• Heartbeat - short message exchange to monitor system health

• HA Framework monitors common system level resources– Volumes, File systems, network interfaces

• Application specific agents monitor application health

• Cluster management tools

TMIn case of a failure

Failure detected by• storage processors within storage system

• Internode communication failure

• monitors detect resource / application malfunction

TMIn case of a failure - Recovery Steps

• Failure notification to administrator

• Storage access attempt via alternate path

• Service and other necessary resource failover based on predefined failover policies

• I/O fencing to prevent any possibility of data

corruption from failing node

TMIssues to consider

Application cleanup and restart time contribute directly to service downtime

False failovers due to timeouts Mechanisms to avoid it– Conservative Timeouts– Multiple monitoring methods

Shared vs. non-shared data access

TMLinux and High availability

Today, • Linux very popular in Internet server space

• Availability needs of a different flavor

• Software packages addressing HA needs in this segment:– Watchdog (www.wizard.de)– RSF-1 from RSI (www.rsi.co.uk)– Understudy from polyserve(www.polyserve.com)– Some work going on in Linux community, related to Heartbeat etc– Red Hat 6.1

TMLinux and High Availability

As Linux matures, it is expected to make way into:Database serversFile servers and Enterprise applicationsand more...

Important Contributing Technologies– High Availability Framework– Enterprise class HA features– Cluster management - Single System View– Journalled Filesystem

· SGI’s XFS going open-source!

TMClustered, Journalled Filesystem

• Seamless sharing of data• No failover of data required• Near-local file system performance

– Direct data channels between disks and nodes

Clustered XFS (CXFS) :• A shareable high-performance XFS file system

– CXFS sits on top of XFS: Fast XFS features

• A resilient file system– Failure of a node in the cluster does not prevent access to the disks from

other nodes

TMInternet server farm

Web server farms

Download servers

Email server farms

Internet Load balancingswitch

TMInternet server farmManageability of a cluster

• Load sharing switch– Hybrid HA and Throughput solutions– Currently minimal feedback from backend to switch– Efforts in place to provide active feedback to switch

· E.g. Cisco’s Dynamic Feedback Protocol

• Performance monitoring

• Cluster management - Single entity view

TMThroughput clustersComputational workload

Engineering/Marketing scenario analysis servers

EDA server farms

Render Farms

Important Technologies• Cluster wide resource management

• Performance monitoring

• Accounting tools

• Cluster management - Single System View

TMThroughput clustersCluster resource management software

Software to optimally distribute independent jobs on independent servers in a cluster

· a.k.a. job scheduler, load sharing software …

• Portable Batch System (PBS)– Open-source software– Developed at NASA – Jobs submitted specifying resource requirements– Jobs run when resources are available subject to

constraints on maximum resource usage– Unified interface to all computing resources

TM

Beowulf : A Beowulf parallel computer is a cluster of standard computer components, dedicated to use for parallel computation and running software that allows the system to be viewed as a unified parallel computer system.

• Coarse-grain parallel computation and communication-based applications

• Popular with academic and research communities• Breaking into commercial environments

Linux Capability Clusters

TMBeowulf background

Mileposts• 1994: Started with 486s and Ethernet• 1997: Caltech achieves 11 Gflops at SC’97 (140 CPUs)• 1999: Amerada Hess replaces SP2 with 32P Beowulf cluster of

Pentium III’s• 1999: SGI shows 132p Beowulf cluster at Supercomputing 99

– Ohio Supercomputing deploys 132p Beowulf cluster from SGI

TM

Motivation : Solving huge problems using commodity technologies.

Recent popularity because of technology availability :

• Linux Operating System• Price/performance hardware

– Killer Microprocessors– Killer Network Interface Cards (NIC)

• Drivers and Usable Protocols• System and Job Management Software• Parallel Algorithm Maturation• Cluster Application Availability

Linux Capability Clusters

TMCluster friendly applications

• Weather analysis : MM5, ARPS• Engineering analysis :CFD, NVH, Crash• Bioinformatics and Sciences

– GAMESS– Zues-MP: Pure Hydro– AS-PCG: 2D Navier-Stokes– Cactus: 3-D Einstein GR Equations– QMC: Quantum Monte Carlo– MILC: QCD

TM

Important technologies:

• Parallel programming environment– MPI : Widely-supported, highly detailed specification of a standard

C and Fortran interface for message-passing parallel programming– Parallel Debugger

· Totalview from Etnus

• Fast interconnects– Commodity or special-purpose NICs– OS bypass implementations of protocols

Linux Capability Clusters

TM

Interconnect (Myrinet)

32 servers

SGI™ 1400 Beowulf Cluster @ OSC

Configuration:

MPI Myrinet Bypass

Head Node

User Community

TMSGI Beowulf ClusterSample Config

TMInterconnect considerations

Latency: • Key Measure : Round Trip Time measured using the

API(e.g. MPI), not hardware latency

Bandwidth: Measured using the API

CPU Overhead:– How much of API/Protocol is buried in the NIC

TM

Interconnect technologyAPI to Adapter

Cluster API Support, Protocols, Network Drivers and Interfaces: • MPI-LAM / TCP-IP / Fast Ethernet• MPICH / GM / Myrinet • MPI/Pro / VIA / Giganet• SGI-MPI / ST / GSN : Currently SGI MIPS only

GSN: Gigabyte System Network

ST: Schedule Transfer (Protocol)

TMCluster Interconnects

Network Hardware• Fast Ethernet• Gigabit Ethernet• Myrinet• GiganetTM

• GSN

Choice of network is highly application dependent

TMScheduled Transfer Protocol(STP)

• Transaction based communication protocol for low latency system area networking

• Extension of DMA to the network• Low CPU utilization and low latency• Data link layer independent• Standard specifies encapsulation for Ethernet, GSN,

ATM ...

TMCluster Interconnect Comparison1 Gbps range

Latency(one way)

Cost ofNIC

Switchcost

Myrinet MPI 18us $1400 $300/port

Giganet MPI 25us $800 $800/port

GigE(Copper)

MPI >100us $500 $300/port

TMMyrinet

• High performance packet switching interconnect technology for clusters

• Bandwidth upto 1.1 Gb/s

• Myricom supported GM is provided for NT/Linux/Solaris/Tru64/VxWorks

• Supports MPI

• Low CPU and latency(MPI--> 18us)

TMReally Fast Interconnects!API to Adapter

MPI/ST/GSN • The technology used on the ASCI Blue Mountain

and other ultra-high-end clusters• ST Protocol : Light-weight ANSI standard protocol

specialized for high-performance clusters• We are working hard to bring ST to Linux and

Gigabit Ethernet.

TMWhat Is GSN?

• ANSI standard interconnect– Highest bandwidth and lowest latency interconnect

standard

• Gigabyte-per-second links, switches, adapters– Provides full duplex dual, 6.4 Gbps (800MB/s) of error-

free, flow controlled data

• Multi-vendor, multi-protocol interoperability– IBM, Compaq, and others to provide full connectivity

TMCompute cluster components Nodes

• Node Width: ?-way SMP

• Special Serves Nodes:– I/O Nodes– Visualization– Front End– Cluster Management

• Node Qualities:– Form Factor– Remote Monitoring– I/O Performance

TMThin Node Cluster

CPU

CPU

I/OX

X: Internal Bus or Crossbar

CPU

CPU

I/O X

Switch

CPU

CPU

I/OX

CPU

CPU

I/O X

TMScalable Hybrid Architecture:Fat Node Cluster

CPU

CPU

I/OX

Internal Bus, Crossbar or Scalable Interconnect

CPU

CPU

I/O XCPU

CPU

CPU

CPU

Switch

CPU

CPU

I/OX

CPU

CPU

I/O XCPU

CPU

CPU

CPU

X:

TMScalable Hybrid Architecture:

• Scalable Internal Interconnect

• Scalable External Network– Switch– Multiple External Network Devices

• Cluster API: MPI– Use Internal Interconnect ONLY on communication

within a node– Support Use of Multiple External Network devices– Multiple Threads Communicating Increases Message

Passing Bandwidth.

TMFat Node Advantages

Larger Shared Memory environment:• More Applications

• Higher Performance Potential– Shared Memory Latencies/Bandwidths– Add parallelism to supporting applications

• Easier System Administration

Less complex, Fatter network:• Fewer wires, higher bandwidth

Require MPI mixed mode support

TMHybrid Programming Models

Parallelism Granularity and Implementation Layers for Hybrid MPI/OpenMP

• OpenMP -> MPI --> MPI/OpenMP– Automatic Parallelization: Based on OpenMP

Library– OpenMP: Loop Level: Fine Grain– OpenMP: Threaded Implementations: Course

Grain– MPI: Course Grain– MPI/OpenMP: Course Grain/Fine Grain

TMSGI Advanced Cluster Environment (ACE)Comprehensive compute cluster package

• Programming Environment

• Load Sharing and Scheduling Tools

• Administration Tools - Single System View

• Performance Management Tools

• Interconnect drivers

• Cluster-wide accounting

• Shared File System

• High Availability Framework

• Professional/Managed Services

TMSummary

• Linux clusters provide– A wide range of computing options

· High Availability· Throughput· Capacity

– Flexibility– Price/performance– Expandability

• ‘Best solution’ requires integration of commodity systems, open source solutions and specific value-add components