a brief overview about distributed systems group a4 chris sun bryan maden min fang
TRANSCRIPT
A brief overview about
Distributed Systems
Group A4
Chris SunBryan MadenMin Fang
Why we need distributed system?
Computers become cheaper
More computers exist
Share resources
Connected together
Centralized v.s. Distributed systems
Mainframes Computerclusters
Characteristics
A collection of independent computers connected through networks.
Characteristics
Providing a single coherent system to users.
hiding the difference between computers and the communications.
Characteristics
Easy to expand and scale.
Replacing, add, and deletecomponents
Characteristics
Middleware
An additional layer of software to hide the heterogeneity of underlying platforms from applications
Middleware
Characteristics
Data flow control is more important than computing.
I/O bound task
CharacteristicsNot proper for tasks of large computing.
A single computer is more efficient for computing.
Problem division and solution combination
Characteristics
LAN or WAN
Goals
Connecting
Transparency
Open
Scalable
Connecting
Easy to share resource
Economics
Transparency
Hide difference in data representation and how a
resource is accessed
Access
Transparency
Hide where a resource is located
Location
Logic Name
Transparency
Hide that a resource may move to another location
Migration
Transparency
Hide that a resource may be moved to another location while in use
Relocation
Transparency
Hide that a resource is replicated
Replication
Transparency
Hide that a resource may be shared by several competitive users
Concurrency
Locking
Transparency
Hide the failure and recovery of a resource
Failure
Transparency
Hide whether a (software) resource is in
memory or on disk
Persistence
Open
Offer services according to standard rules that describe the system and
semantics of those services
Protocol and IDL
Open
Flexible
Separating policy and mechanism
Rich set of parameters
Increase complexity
Scalable
Size
Geography
Administration
Scalable
Decentralization
Data Services Algorithms
Scalable
Techniques
Async Distributed Replicate
DNS zones Cache
Hardware types
Multiprocessor
A single physical address space shared by all CPUs
Multiprocessor
Bus
Coherent
Overloaded
Multiprocessor
Cache
90% hit rate
512K~1M
Multiprocessor
Crossbar
N2
Multiprocessor
Omega
N/2log2 N
Multicomputer
Each machine has its own private memory
MulticomputerHomogeneous
OS Network Memory
Parallel
Multicomputer
Bus
Ethernet
25~100 nodes
Multicomputer
Switch
Mesh Hypercube
Multicomputer
Hypercube
Dimension = N
# Node = 2N
# Link = k2k-1
Multicomputer
Physical routing distance
Hamming distance
Types of Architectures
• Bus • Fully Connected• Ring• 2D
– Grid
– Torus
• HyperCube• Fully connected
2D - Grid
• Grid or mesh– Matrix– Switches are connected to many other switches
but only one processor.
SwitchProcessor
2D - Torus
• Each column is a ring
• Each row is a ring.
• More connections – more communication.
SwitchProcessor
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 con
nection between nodes.
– Grid = 4
– Torus = 8
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)
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.
References
• Computer Architecture – A Quantitative Approach. Second Edition, Hennessy & Patterson, Morgan Kaufmann, 1996.
The End