DISTRIBUTED FILE SYSTEM

1. DISTRIBUTED FILE SYSTEM Presented By: Payal Patel From Group-1

2. DISTRIBUTED FILE SYSTEM • It is a client-server based application. • organizes file and directory services of individual servers into a global directory. • organization is hierarchical and directory-based. • use file or database replication (distributing copies of data on multiple servers) to protect against data access failures.

3. DISTRIBUTED FILE SYSTEM FEATURES • Easy access to files • Availability • Server load balancing • File and folder security

4. DFS IN CLIENT-SERVER MODEL • Services provided by server are: • Management of shared resources • Management of backup and recovery • User mobility • Diskless workstations

5. DFS: NAMING • Location transparency: • The path name does not reveal the file location. e.g.:/serverA/dir1/dir2/X does not say where the server is located.

6. NAMING • Location independence: • Files can be moved and all references to them continue to be valid. e.g.: /serverA/dir1/dir2/X is not location independent.

7. TWO-LEVEL NAMING • Symbolic Names : • Human readable. e.g.:/courses/slides/files.ps • Binary Names: • Machine readable names. • Easier to manipulate. e.g.: UNIX i-node,or server IP address :I-node number.

8. WORKING MODEL OF CLIENT-SERVER Application interface Logical file system Remote access Logical file system Block buffer management Client interface Server interface Block buffer management Virtual disk Device management Device management Server Client Network

9. WORKING MODEL OF CLIENT-SERVER • Logical file system • Block buffer management • Device management • Application interface/System call interface • Client/Server interface

10. FILE SERVICE INTERFACE • Remote Access Model • Only the needed blocks of files are retrieved from the server. • Once the client is done with a block,it is written back to the server. • Example:NSF Read Block Write Block server client

11. FILE SERVICE INTERFACE • Upload/Download Model • Entire files are retrieved from the server,and accessed at the client. • Once the client is done ,the file is stored back at the server. • Typical mass storage systems:e.g.Unitree. Get file Put file client Server

12. GRANULARITY LEVELS OF FILE ACCESS • File-level storage and retrieval • Block level(sometimes called page level) • Byte level

13. EXAMPLES OF DFS • Network File System(NFS) • Developed by Sun microsystems. • Provide transparent,remote access to file systems. • Defines two client-server protocols.

14. Andrew File System(AFS) • Developed at Carnegie Mellon University. • Entire contents of files are transmitted to client computers by AFS servers. • Use virtual disk abstraction.

15. CHARACTERISTICS OF AFS • most files are small--transfer files rather than disk blocks. • reading more common than writing • most access is sequential • most files have a short lifetime--lots of applications generate temporary files (such as a compiler).

16. file sharing (involving writes) is unusual--argues for client caching • processes use few files • files can be divided into classes--handle ``system'' files and ``user'' files differently.

17. WebNFS • It is an extension to the NFS server to overcome the drawbacks of NFS. • Drawbacks of the NFS that WebNFS solves are: • First implementation used UDP only. • Portmapping required awkward for firewalls and proxies. • Separate mount protocol requirement. • Allows java applets to access files stored on the servers.

18. Transparent Cryptographic File System(TCFS) • Developed as an extension to the NFS in order to provide a robust security mechanism . • File contents is guaranteed by means of the Data Encryption standard(DES). • To provide security mechanism ,secure files should not be readable by: • Users other that the legitimate owner. • Tapping the communication lines between the user and the remote file system server. • The superuser of the file system server.

19. THE REMOTE FILE SHARING SYSTEM • developed by AT&T to allow UNIX workstations to share files over a network. • provides access to files and directories without the user having to know where the resource is located. • allows users to mount special directories so that they can share devices (e.g. tape drives) residing on other machines.

20. RFS • It is stateful protocol. The server maintains state information of local resources • can NOT be used to boot diskless clients. • does NOT support symbolic linking or automounting.

21. CODA DFS • developed in the group of M. Satyanarayanan at Carnegie Mellon University • Coda incorporates many features not found in other systems:Mobile Computing.

22. FEATURES OF CODA • disconnected operation for mobile clients • reintegration of data from disconnected clients. • bandwidth adaptation . • Performance and scalability • client side persistent caching of files, directories and attributes for high performance • write back caching.

23. Failure Resilience • read/write replication servers • resolution of server/server conflicts • handles of network failures which partition the servers • handles disconnection of clients client • Security • kerberos like authentication • access control lists (ACL's)

24. THANK YOU