Post on 01-Apr-2015
transcript
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