Chapter 11 Modern Computer Systems Clusters and Networks

Chapter 11 Modern Computer Systems, Clusters, and Networks The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3 rd Edition, Irv Englander John Wiley and Sons 2003

Basic Personal Computer System Chapter 11: Modern Computer Systems, Clusters, and Networks 2

Mainframe Computer System Chapter 11: Modern Computer Systems, Clusters, and Networks 3

Major PC System Components Chapter 11: Modern Computer Systems, Clusters, and Networks 4

System Performance Improvements § § § Multiple CPUs Faster clock speed, buses and circuits Wider instruction and data paths Faster disk access More and faster memory Chapter 11: Modern Computer Systems, Clusters, and Networks 5

Multiprocessing § Reasons § Increase the processing power of a system § Parallel processing § Types of multiprocessor systems § Tightly coupled systems § Loosely coupled systems Chapter 11: Modern Computer Systems, Clusters, and Networks 6

Tightly Coupled Systems § Also called multiprocessor systems § Identical access to programs, data, shared memory, I/O, etc. § Easily extends multi-tasking, and redundant program execution § Two ways to configure § Master-slave multiprocessing § Symmetrical multiprocessing (SMP) Chapter 11: Modern Computer Systems, Clusters, and Networks 7

Tightly Coupled Systems Chapter 11: Modern Computer Systems, Clusters, and Networks 8

Master-Slave Multiprocessing § Master CPU § Manages the system § Controls all resources and scheduling § Assigns tasks to slave CPUs § Advantages § Simplicity § Protection of system and data § Disadvantages § Master CPU becomes a bottleneck § Reliability issues – if master CPU fails entire system fails Chapter 11: Modern Computer Systems, Clusters, and Networks 9

Symmetrical Multiprocessing § Each CPU has equal access to resources § Each CPU determines what to run using a standard algorithm § Disadvantages § Resource conflicts – memory, i/o, etc. § Complex implementation § Advantages § High reliability § Fault tolerant support is straightforward § Balanced workload Chapter 11: Modern Computer Systems, Clusters, and Networks 10

Loosely Coupled Systems § Clusters or multi-computer systems § Each system has its own CPU, memory, and I/O facilities § Each system is known as a node of the cluster § Advantages § Fault-tolerant, scalable, well balanced, distance is not an issue § Two ways to configure § Shared-nothing model § Shared-disk model Chapter 11: Modern Computer Systems, Clusters, and Networks 11

Shared-Nothing Model § High speed link between nodes § No sharing of resources § Partitioning of work through division of data § Advantage § Reduced communication between nodes § Disadvantage § Can result in inefficient division of work Chapter 11: Modern Computer Systems, Clusters, and Networks 12

Shared-Disk Model § High speed link between nodes § Disk drives are shared between nodes § Advantage § Better load balancing § Disadvantage § Complex software required for transactional processing (lock, commit phases) Chapter 11: Modern Computer Systems, Clusters, and Networks 13

Cluster Models Chapter 11: Modern Computer Systems, Clusters, and Networks 14

Beowulf Clusters § Simple and highly configurable § Low cost § Networked § Computers connected to one another by a private Ethernet network § Connection to an external network is through a single gateway computer § Configuration § COTS – Commodity-off-the-shelf components such as inexpensive computers § Blade components – computers mounted on a motherboard that are plugged into connectors on a rack § Either shared-disk or shared-nothing model Chapter 11: Modern Computer Systems, Clusters, and Networks 15

Blade and Rack of Beowulf Cluster Figure 11. 9 Chapter 11: Modern Computer Systems, Clusters, and Networks 16

Computer Interconnection § Communication channel – pathway for data movement between computers § Point-to-Point connectivity § Communication channel that passes data directly between two computers § Serial connection § Telephone modem § Terminal controller – handles multiple point-topoint connections for a host computer § Multipoint connectivity § Multidrop channel or shared communication channel Chapter 11: Modern Computer Systems, Clusters, and Networks 17

Example: Point-to-Point Chapter 11: Modern Computer Systems, Clusters, and Networks 18

Client-Server Architecture § Computer servers provides services § File storage, databases, printing services, login services, web services § Client computers § Execute programs in its own memory § Access files either locally or can request files from a server Chapter 11: Modern Computer Systems, Clusters, and Networks 19

Client-Server Network Chapter 11: Modern Computer Systems, Clusters, and Networks 20

LAN Topology § Arrangement of workstations in a shared medium environment § Logical arrangement (data flow) § Physical arrangement (cabling scheme) Chapter 11: Modern Computer Systems, Clusters, and Networks 21

LAN Topologies: Bus § Multipoint medium § Stations attach to linear medium (bus) using tap § Transmission from any stations travels entire medium (both directions) § Termination required at ends of bus to prevent the signal from bouncing § Break in cable brings down entire bus Chapter 11: Modern Computer Systems, Clusters, and Networks 22

Bus LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks 23

LAN Topologies: Tree § Generalization of bus topology § Branching cable with no closed loops § Cable(s) begin at headend, travel to branches which may have branches of their own § Each transmission propagates through network, can be received by any station Chapter 11: Modern Computer Systems, Clusters, and Networks 24

LAN Topologies: Ring § Repeaters are joined by unidirectional point-to-point links in a ring § As data circulates past a receiver, the receiver checks its address, and copies those intended for it into a local buffer § Data circulates until it returns to source, which removes it from network § Better performance at high levels of usage Chapter 11: Modern Computer Systems, Clusters, and Networks 25

Ring LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks 26

LAN Topologies: Star § Each station connected point-to-point to a central station, usually with two undirectional links § Switching in the central station connects pairs of nodes together § Central node can broadcast info, or can switch frames among stations § Failure of central station causes entire network to go down Chapter 11: Modern Computer Systems, Clusters, and Networks 27

Star LAN Diagram Chapter 11: Modern Computer Systems, Clusters, and Networks 28

Ethernet MAC Protocol § MAC – Medium Access Control § Ethernet and CSMA/CD § Carrier sense multiple access with collision detection § Four step procedure § § If medium is idle, transmit If medium is busy, listen until idle and then transmit If collision is detected, cease transmitting After a collision, wait a random amount of time before retransmitting Chapter 11: Modern Computer Systems, Clusters, and Networks 29

Ethernet Frame Chapter 11: Modern Computer Systems, Clusters, and Networks 30

Switched Ethernet Chapter 11: Modern Computer Systems, Clusters, and Networks 31

Token Ring MAC Protocol § Token “seized” by changing a bit on the circulating frame to indicate start of frame rather than token § Default configuration requires sender to complete transmission and begin receiving transmitted frame before releasing the token § “Early token release” allows release of token after transmission but before receipt of frame Chapter 11: Modern Computer Systems, Clusters, and Networks 32

Hubs § The active central element of the star layout. § When a single station transmits, the hub repeats the signal on the outgoing line to each station. § Hubs can be cascaded in a hierarchical configuration § Ethernet hubs are physically a star but logically a bus. Chapter 11: Modern Computer Systems, Clusters, and Networks 33

Bridges § Allow connections between LANs and to WANs § Used between similar networks § Read all frames from each network § Accept frames from sender on one network that are addressed to a receiver on the other network § Retransmit frames from sender using MAC protocol for receiver Chapter 11: Modern Computer Systems, Clusters, and Networks 34

Routers § Similar to bridges but connect dissimilar networks § Convert format of the message to correspond to the protocol of the other network § Network traffic is specifically addressed to the router Chapter 11: Modern Computer Systems, Clusters, and Networks 35

Wide Area Network § Circuit switching § Dedicated channel between source and destination for duration of connection § Message switching § Dedicated channel for an entire message § Packet switching § An independent path is created for each datagram § Virtual circuit switching § A route is created from source to destination before transmission begins and all datagrams are sent using the same route Chapter 11: Modern Computer Systems, Clusters, and Networks 36

Networks vs. Clusters § Externally, clusters appear as a single computing unit. § Network nodes are individually identifiable. § Workload on a cluster is determined by cluster administration and loadbalancing software. § Networkload cannot be controlled using the above method. Chapter 11: Modern Computer Systems, Clusters, and Networks 37

High Performance Computing § Massively parallel processor architectures (MPP) § Clusters of power machines or larger Beowulf blade clusters § Well suited for problems that can be broken into subtasks § Grid computing § Supercomputer performance through distributing CPU processing to the spare CPU cycles of personal computers connected to a network Chapter 11: Modern Computer Systems, Clusters, and Networks 38

Parallel Computers § § Massively parallel architectures Hundreds to millions of CPUs have small amounts of local memory All CPUs have access to global shared memory § Pipelined CPUs § Results from one CPU flow to the next CPU for additional processing Chapter 11: Modern Computer Systems, Clusters, and Networks 39