/DistributedFilesystem

Primary LanguagePython

#Distributed Filesystem This filesystem operates using an upload/download model. It's components are: a distributed filesystem, a directory service, replication, and a lock service.

##Components:

  • Node: An ordinary fileserver node
    • Stores files in a directory hierarchy matching that of the entire filesystem, even if the node only stores files in one sub-directory
    • Advertises its contents to the Directory Server on startup
    • Advertises its identity to the Replication Manager on startup
  • DirectoryServer: Directory Server node
    • Authoritative source on the hierarchy of the filesystem and the location of each file
    • Sends information about the contents of the filesystem and the location of files to clients that request it
    • Doesn't actually store or transfer files, just metadata
  • ReplicationManager: Replication Manager server
    • Assigns each Node to a replication set
    • Responds to queries from nodes requesting the identity of other nodes in their set
  • LockServer: Locking server
    • Provides a means for clients to guarantee unique access to a file or folder in the filesystem

##Usage: A sample client usage of the filesystem:

  1. Client contacts the Directory Server to list all files in the / directory.
  2. The client decides to modify /thesis.txt, so he requests the location of that file from the Directory Server.
  • The Directory Server will reply with just one of the locations of the file. Due to replication, the file may be located on multiple servers.
  1. Client contacts the Lock Server to lock /thesis.txt so he can download it without any other clients being able to edit it.
  • If the client cannot immediately obtain the lock, it must wait until the lock becomes free.
  1. The client then contacts the node location received in step 2 and downloads the file.
  2. The client modifies the file as needed.
  3. The client contact the Directory Server again to find the location of /thesis.txt.
  • This is necessary because the node that the client downloaded the file from in step 4 may now have left the network, or may be part of a different replication set.
  1. Client uploads the modified file to the location it received from step 6.
  2. The client contacts the Lock Server again to unlock /thesis.txt.

Note: client actions can be simulated using the tester.py file.