1. A brief overview about Distributed Systems Group A4 Chris Sun Bryan Maden Min Fang

2. Why we need distributed system? Computers become cheaper More computers exist Share resourcesConnected together

3. Centralized v.s. Distributed systems Mainframes Computer clusters

4. Characteristics A collection of independent computers connected through networks.

5. Characteristics Providing a single coherent system to users. hiding the difference between computers and the communications.

6. Characteristics Easy to expand and scale. Replacing, add, and delete components

7. Characteristics Middleware An additional layer of software to hide the heterogeneity of underlying platforms from applications

8. Middleware

9. Characteristics Data flow control is more important than computing. I/O bound task

10. Characteristics Not proper for tasks of large computing. A single computer is more efficient for computing. Problem division and solution combination

11. Characteristics LAN or WAN

12. Goals Connecting Transparency Open Scalable

13. Connecting Easy to share resource Economics

14. Transparency Hide difference in data representation and how a resource is accessed Access

15. Transparency Hide where a resource is located Location Logic Name

16. Transparency Hide that a resource may move to another location Migration

17. Transparency Hide that a resource may be moved to another location while in use Relocation

18. Transparency Hide that a resource is replicated Replication

19. Transparency Hide that a resource may be shared by several competitive users Concurrency Locking

20. Transparency Hide the failure and recovery of a resource Failure

21. Transparency Hide whether a (software) resource is in memory or on disk Persistence

22. Open Offer services according to standard rules that describe the system and semantics of those services Protocol and IDL

23. Open Flexible Separating policy and mechanism Rich set of parameters Increase complexity

24. Scalable Size Geography Administration

25. Scalable Decentralization DataServicesAlgorithms

26. Scalable Techniques AsyncDistributedReplicate DNS zonesCache

27. Hardware types

28. Multiprocessor A single physical address space shared by all CPUs

29. Multiprocessor Bus Coherent Overloaded

30. Multiprocessor Cache 90% hit rate 512K~1M

31. Multiprocessor Crossbar N2N2

32. Multiprocessor Omega N/2log 2 N

33. Multicomputer Each machine has its own private memory

34. Multicomputer Homogeneous OSNetworkMemory Parallel

35. Multicomputer Bus Ethernet 25~100 nodes

36. Multicomputer Switch MeshHypercube

37. Multicomputer Hypercube Dimension = N # Node = 2 N # Link = k2 k-1

38. Multicomputer Physical routing distance Hamming distance

39. Types of Architectures Bus Fully Connected Ring 2D –Grid –Torus HyperCube Fully connected

40. 2D - Grid Grid or mesh –Matrix –Switches are connected to many other switches but only one processor. Switch Processor

41. 2D - Torus Each column is a ring Each row is a ring. More connections – more communication. Switch Processor

42. Bandwidth Bisection Bandwidth –Separate network into two halves. –Sum the bandwidth of the lines crossing the imaginary dividing line. Examples: –Bus has Bisection Bandwidth of one since only one connection between nodes. –Grid = 4 –Torus = 8

43. Fault Tolerance The bigger the bandwidth the better the fault tolerance. Bus network has low fault tolerance. –When the bus is down, the communication is down. Fully connected network has highest fault tolerance. –Also most expensive. (messaging, hardware)

44. Leads to … Grid networks are starting to be developed to share processors and act as a single unit. Applications in Gaming, workplace. –Users have more computing power at less cost. –Users in one time zone can use grid in other time zone where those users are asleep. Continual use of computing power.

45. References Computer Architecture – A Quantitative Approach. Second Edition, Hennessy & Patterson, Morgan Kaufmann, 1996.

46. The End