Distributed Computing. Santa Clara University 2016

Transcription

1 Distributed Computing Santa Clara University 2016

2 Generations of Computers : Mainframes : Mini-computers (PDP11, VAX) : Personal computers with VLSI μ- processors : Portable computing and pervasive systems ? : High Performance Computing (HPC)/ High Throughput Computing (HTC) in clusters, grids or clouds ? : Utility Computing?

3 Trends: HPC - HTC HPC Massively Parallel Processors (MPP) give way to clusters HTC High flux computing For internet searches and other services accessed by millions of users simultaneously Problems: Costs, Energy, Security, Reliability Measured by: Efficiency, Dependability, Adaptation in the programming model, Flexibility in application development

4 Trends: Utility Comuting

5 Trends: Utility Computing Utility computing: Internet of things Cyber-physical systems Merges Computation, Communication, Control Examples: Electrical grid, car, G5 cell phones

6 Hype Cycle Gartner s 2010 Hype Cycle Special Report Evaluates Maturity of 1,800 Technologies, 7 Oct. 2010

7 Computer Architecture Memory wall: Processors consume more data (multi-core) Memory becomes bigger, but not faster Disks change role: Areal density increases between % annually Much less growth in throughput Technology shifts Shingled write (shipping) HAMR Two-dimensional

8 CPU - Network Speed

9 Memory vs Disk Capacities Tape units are dead, disks are tape units, flashes are disks, and memory are caches now. Jim Gray

10 Virtual Machine Modes

11 Virtual Machine Modes Virtual Machine: Runs any OS Middleware layer: Virtual Machine Monitor Native VM VMM runs as part of the system OS is modified Bare metal supervisor: VMM handles CPU, memory, I/O directly Example: Hypervisor is Xen system

12 Virtual Machine Modes Hosted VM VMM runs as an application Simulates access to hardware resources

13 Classical Distributed Systems

14 Definition A distributed system is a collection of independent computers that appears to its users as a single coherent system. A system in which I cannot use my machine because of the malfunction of another system of which I did not know that it existed.

15 Definition A distributed system is often organized as middleware that stretches over several systems

16 Definition Characteristics of a distributed system Transparency Openness: DS offers services according to standard rules Can use an Interface Definition Language IDL Interoperability Portability Experience suggests: Separate policies from mechanisms Example: Cache policy in WWW browsers is set by users Scalability

17 Transparency Access Location Migration Relocation Replication Concurrency Fault Persistence Hide differences in data representation and access to resources Hide the site of a resource Hide the migration of a resource to a different site Hide the migration of a resource to a different site while it is being used Hide the fact that a resource is replicated. Hide that a resource is used by different entities Hide faults and recovery from faults Hide whether a resource is in memory or stable storage. NB: There is often a trade-off between transparency and performance

18 Scalability Problems Concept Example Centralized services A single server for all users Centralized data A single on-line telephone book Centralized algorithms Doing routing based on complete information Examples of scalability limitations.

19 Hardware Concepts 1.6 Different basic organizations and memories in distributed computer systems

20 Multiprocessors (1) A bus-based multiprocessor.

21 Multiprocessors (2) a) A crossbar switch b) An omega switching network

22 Hardware Concepts Different Organizations for Processors and Memories

23 Architectures for Multiprocessors Bus-based architecture

24 Architectures for Multiprocessors (a) Crossbar switch (b) An omega switching network

25 Homogeneous Multicomputer Systems (a) Organized as a grid (b)organized as a hypercube

26 Software concepts for classical distributed systems DOS Tightly coupled operating system for multiprocessors and homogeneous multicomputers Hide and manage hardware resources NOS Loosely coupled operating system for heterogeneous multicomputers (LAN and WAN) Offer local services to remote clients Middleware Additional layer atop of NOS implementing general-purpose services Provide distributed transparency

27 Uniprocessor Operating Systems Separating applications from operating system code through a microkernel