Distributed File System
Terminology
- service, server, client --- client interface (primitive file ops)
- DFS --- file system whose clients/servers/storage devices are dispersed among the machines of a distributed system.
- diskless machines on network
Naming and Transparency
- Naming -- mapping between logical and physical devices.
- Transparency -- "Hiding" where a file is located. Possible replication for efficiency/safety.
- Location Transparency -- file name does not reveal physical location.
- Location Independence -- name does not change when file physically moved. (can now share data, good abstraction, avoid network topology issues)
Naming schemes:
- "host:local-name"
- attach remote dirs to local dirs (Sun's NFS)
- total integration --- hard to do
Remote File Access
Remote Service(RPC):
- heavy network load.
- system mirrors local file system interface.
Caching:
NFS is a hybrid of the two.
Stateful/Stateless service
stateful -- system keeps track of open files, local file pointers, etc. Fast, but difficult to restore after crashes.
stateless -- each service call is a contained entity. Slow but safe.
Network File System (NFS)
Mount operations -- a remote directory is mounted over a directory of the local file system. Local directory becomes the root of the remote directory. Once set up all accesses to remote files are transparent.
Protocol(RPC's):
- Searching for a file.
- Reading dir entries.
- Manipulating links and directories.
- Accessing file attributes.
- Reading and writing files.
Virtual File System -- vnodes vs inodes.
Copyright ©2014, G. Hill Price
Send comments to G. Hill Price