CHARACTERISTICS OF DISTRIBUTED FILE

SYSTEMS

PHANI VAMSI KRISHNA.MADDALI

BASIC CONCEPTS..

FILE SYSTEMS: It is a method for

storing and organizing computer files

and the data they contain to make it

easy to find and access them.

DISTRIBUTED File System : A DFS is a network file

system where a single file system can be distributed across

several physical computer nodes. Separate nodes have

direct access to only a part of the entire file system, in

contrast to shared disk file systems where all nodes have

uniform direct access to the entire storage.

QUIZ TIME YES=1; NO=0.

Are u able to access the GSU website?

Are u able to access the website from any system that has got an internet connection?

You don’t know from what particular server you are accessing the website.

Are you and your friend able to access the website at the same time?

WHATZ YOUR SCORE??

You are not able to know about the server updates?

Are you able to access the website from both MAC OS and Windows Vista?

You cannot know the number of added student accounts of the student web mail?

Compare the Results.!!!

CHARACTERISTICS OF DISTRIBUTED FS :

The 2 key characteristics are:

Dispersion Dispersed Clients Dispersed Files

Multiplicity Multiplicity Of Users Multiplicity Of Clients

A Transparent* DFS should possess few properties.

Transparency*:operating in such a way as to not be perceived by users.

TRANSPARENCY PROPERTIES:

Login Transparency: User can log in at any host with uniform login procedure and perceive a uniform

view of the file system.

Access Transparency: Client process on a hots has uniform mechanism to access all files in system regardeless of files are on local/remote host.

Location Transparency: The names of the files do

not reveal their physical location.

DESIRABLE CHARACTERISTICS: Concurrency Transparency: An update to a file

should not have effect on the correct execution of other process that is concurrently sharing a file.

Replication Transparency: Files may be replicated to provide redundancy for availability and also to permit concurrent access for efficiency.

Fault Tolerance.

Scalability.

Heterogeneity of the Systems.

FAULT TOLERANCE.

It is a design that enables a system

to continue operation, possibly at a

reduced level, rather than failing

completely, when some part of the

system fails.

Possible Solution:REDUNDANCY

How critical is the component?

How likely is the component to fail?

How expensive is it to make the component fault-tolerant?

OTHER CHARACTERISTICS INCLUDE:

Network Transparency: Same access operation as if they are local files.

Location Independence: The file name should not be changed when the physical location of the file changes.

User Mobility: User should be able to access the file from any where.

File Mobility: Moves files from one place to the other in a running system.

FEW EXAMPLES

The GOOGLE File System: A scalable distributed file

system for large distributed data-intensive

applications. It provides fault tolerance while running

on inexpensive commodity hardware, and it delivers

high aggregate performance to a large number of

clients.

The CODA distributed file system: Developed at

CMU, incorporates many distinguished features which

are not present in any other distributed file system.

CHARACTERISTICS OF CODA DFS:

disconnected operation for mobile clients

reintegration of data from disconnected clients

bandwidth adaptation

Failure Resilience

read/write replication servers

resolution of server/server conflicts

handles of network failures which partition the

servers

handles disconnection of clients client

CHARACTERISTICS CONTINUED…

Performance and scalability

client side persistent caching of files, directories

and attributes for high performance

write back caching

Security

kerberos like authentication

access control lists (ACL's)

Well defined semantics of sharing

Freely available source code

REFERENCES

Distributed Operating Systems & Algorithms, by

Randy Chow and Theodore Johnson, 1997.

http://www.cs.ucdavis.edu/~

wu/ecs251/ecs251_DFS.pdf

http://pages.cs.wisc.edu/~

sschang/OS-Qual/fs/distributed_file_systems.htm

http://www.coda.cs.cmu.edu/ljpaper/lj.html

http://labs.google.com/papers/gfs.html

http://en.wikipedia.org/wiki/Distributed_file_system

QUERIES?

THANK YOU