Simple PEer to peER File System (SPEERFS) Done by: Assaf WaksmanBenny Pano Supervised by: Uri Schonfeld On Spring 2005

Background P2P – A way of sharing information among many equal work stations File System – A database that supports and stores information units called files. A need for sharable space that holds file- system instances arises: Achieves availability of information everywhere, as well as decrease in bandwidth load over a single server.

Objective Designing and implementing a distributed file system with a P2P approach. The system will let a user the ability to mount and use roots, which will be shared among the peers.

Considerations and Assumptions The files are small There are no sudden crashes of peers A peer’s bandwidth is of domestic type There are no simultaneous reads and/or writes to the same file (not including directories)

System’s goal characteristics Scalable P2P network Maintain data integrity Equality among peers Support basic FS operations needed by the OS Ease of use

Architecture overview Find a value’s holder Create / Delete / Write / Read roots, files, directories Interface / Driver Create / Delete roots File-System P2P

NFS Protocol Client  Server relationship Gives the ability for remote users to mount a file system that populates the server Uses the RPC mechanism Supports { READ, WRITE, CREATE, REMOVE, MKDIR, RMDIR, READDIR, etc.} remote procedure calls

Chord Protocol Each peer has a unique value. Each peer has a successor and a predecessor in the network. A peer is responsible for a values’ range between his predecessor and himself. When a new peer joins the network, his successor’s responsibility range is updated accordingly.

Chord Qualities Maintains scalability Search for a value: O(logN) Join / departure of a peer: O((logN)^2) Maintains data integrity and organization

Chord Demonstration

File-System’s Data Structures Every file in the file system is physically stored by the appropriate peer, according to the chord protocol. Each peer has a database file that holds a list of all the files stored by this peer. Each directory in the file system has a physical database file that contains a list of all the content of that directory. The system supports passwords enforcement.

System’s Packages Were made: chord – supports the ChordPeer class com – supports communication operations misc – stores helper classes scome – supports the ScomePeer class Was altered: nfsserver – implements an NFS server and contains the main method Was used: org.acplt.oncrpc – implements the RPC mechanism needed by the NFS server

Major Classes Peer – supports communication’s and basic peer’s functionality. ChordPeer – inherits from Peer and implements the chord protocol. ScomePeer – inherits from Peer and supports file system’s functionality. Listener – Receives messages from other peers and initiates their handling.

Future Improvements Handle simultaneous joins of peers to the chord network Handle hostile messages Support file links in the SCOME layer Support multiple copies of files’ data Limit the amount of data a peer can hold Write a designated driver for the OS Encrypt and compress messages and databases