![BITS Pilani, Pilani Campus
NFS- Transport[1]
• Uses a Request – Response model
– Server receives RPC – Remote Procedure Call –
requests from clients
– Can be run on top of stream (e.g. TCP) or datagram
protocol (e.g. UDP)
• Each RPC message may need to be broken into
multiple packets to be sent across the network.
– May typically require up to 6 packets
– May cause problems in UDP – in case of failure,
entire message must be retransmitted
6](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-6-320.jpg)
![BITS Pilani, Pilani Campus
NFS – Transport[2]
• Remote Procedure Call (RPC)
– Client sees a procedure call interface (akin to a local
procedure call)
– But the call (along with the parameters) is marshalled
into a message and sent over the network
• Marshalling may involve serializing
• Server unmarshalls the message (i.e. separates it
into pieces) and processes it as a local operation.
• The result is similarly marshalled by the server and
sent to the client which in turn unmarshalls it.
7](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-7-320.jpg)
![BITS Pilani, Pilani Campus
NFS- Operation[1]
• NFS protocol is stateless
– Each request is independent
• Server need not maintain information about clients and their
requests
• In practice, server caches recently accessed file
data.
– It improves performance
– and is useful for detecting retrials of previously serviced
requests
• Transaction-Commit semantics implies high
overhead:
– Synchronous writes are required for write operations.
9](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-9-320.jpg)
![BITS Pilani, Pilani Campus
NFS- Operation[2]
• NFS is a client-server protocol
– No discovery or registry is used.
• i.e. client must know the server and the filesystem
– Server’s filesystem has to be exported (by
mounting).
• Refer to mount system call on Unix
• Each server has a globally unique id (guid)
• Client application need not distinguish
between local and remote files
– i.e. once a filesystem is mounted applications use
the same interface for both types of files
10](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-10-320.jpg)
![BITS Pilani, Pilani Campus
NFS - Operation[3]
• NFS is a client-server protocol
– File manager part of client file system remains the same
as that for the local file system
• Only the file store is local or remote
• Each remote file that is active manifests as an
nfsnode in the client’s filesystem
– Recall the active file data structures:
• Per-Process File Descriptor
– Kernel File Entry
– vnode
– file-store-specific data structure
» inode for local file store and
» nfsnode for remote filestore
11](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-11-320.jpg)
![BITS Pilani, Pilani Campus
NFS - Operation
• Basic Protocol (Mounting): Client C, Server S
– C (mount process) -----> S(portmap daemon)
• request port address of mountd
– S (portmap daemon) ----> C
• return the port address of its mountd
– C (mount process) ----> S(mountd daemon)
• request mounting of filesystem [pathname]
– S (mountd daemon):
• get file handle for desired mount point from kernel
– S (mountd daemon) ---> C
• return filehandle of mountpoint OR error
12](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-12-320.jpg)
![BITS Pilani, Pilani Campus
NFS - Operation
• Basic Protocol (I/O Operation): Client C, Server S
– C (app. process): write system call
• Data is copied into kernel buffer and call returns
• nfsiod daemon wakes up
– C (nfsiod daemon) -----> S(nfs_rcv)
• Request write [buffer contents]
– S delegates request to nfsd daemon
• nfsd daemon invokes write on disk and waits for I/O
– S (nfsd daemon) ---> C (nfsiod daemon)
• return ack for the write operation
13](https://image.slidesharecdn.com/m3-nfsfs3-180108063422/85/M3-nfs-fs-3-2-1-13-320.jpg)
M3 nfs fs-3.2.1
- 1. BITS Pilani Pilani Campus Data Storage Technologies & Networks Dr. Virendra Singh Shekhawat Department of Computer Science and Information Systems
- 2. BITS Pilani, Pilani Campus Topics • Network File System protocol (NFS) – Design goals – Interface – NFS Transport – Operation 2
- 3. BITS Pilani, Pilani Campus What is NFS? • A remote file system protocol – Designed and implemented by Sun Microsystems – Provides Unix-like file system interface and semantics • It is implemented as a Client-Server application – Client part imports file systems (from other computers) – Server part exports (local) file systems • i.e. makes it visible on the network and enables access from other computers 3
- 4. BITS Pilani, Pilani Campus NFS Design Goals • Stateless protocol – Increased robustness – easy recovery from failures • Support for Unix filesystem semantics – Also supports other semantics such as MS-DOS • Protection and Access Control same as Unix filesystem semantics • Transport-independent protocol – Originally implemented on top of UDP – Easily moved to TCP later – Has been implemented over many non-IP-based protocols. 4
- 5. BITS Pilani, Pilani Campus NFS Design Limitations • Design for clients and servers connected on a locally fast network. – Does not work well over slow links nor between clients and servers with intervening gateways • Stateless protocol – Session state is not maintained 5
- 6. BITS Pilani, Pilani Campus NFS- Transport[1] • Uses a Request – Response model – Server receives RPC – Remote Procedure Call – requests from clients – Can be run on top of stream (e.g. TCP) or datagram protocol (e.g. UDP) • Each RPC message may need to be broken into multiple packets to be sent across the network. – May typically require up to 6 packets – May cause problems in UDP – in case of failure, entire message must be retransmitted 6
- 7. BITS Pilani, Pilani Campus NFS – Transport[2] • Remote Procedure Call (RPC) – Client sees a procedure call interface (akin to a local procedure call) – But the call (along with the parameters) is marshalled into a message and sent over the network • Marshalling may involve serializing • Server unmarshalls the message (i.e. separates it into pieces) and processes it as a local operation. • The result is similarly marshalled by the server and sent to the client which in turn unmarshalls it. 7
- 8. BITS Pilani, Pilani Campus NFS- Interface • NFS RPC requests – Idempotent Operations(i.e. NFS client may send the same request one or more times without any harmful side effects) • GETATTR, SETATTR, LOOKUP, READLINK, READ, WRITE, CREATE, SYMLINK, READDIR, STATFS – Non-Idempotent Operations • REMOVE, RENAME, LINK, MKDIR, RMDIR • Idempotency is significant because of – slow links and lost RPC acks. • Each file on the server is identified by a globally unique file handle – created when a lookup is sent by client to server 8
- 9. BITS Pilani, Pilani Campus NFS- Operation[1] • NFS protocol is stateless – Each request is independent • Server need not maintain information about clients and their requests • In practice, server caches recently accessed file data. – It improves performance – and is useful for detecting retrials of previously serviced requests • Transaction-Commit semantics implies high overhead: – Synchronous writes are required for write operations. 9
- 10. BITS Pilani, Pilani Campus NFS- Operation[2] • NFS is a client-server protocol – No discovery or registry is used. • i.e. client must know the server and the filesystem – Server’s filesystem has to be exported (by mounting). • Refer to mount system call on Unix • Each server has a globally unique id (guid) • Client application need not distinguish between local and remote files – i.e. once a filesystem is mounted applications use the same interface for both types of files 10
- 11. BITS Pilani, Pilani Campus NFS - Operation[3] • NFS is a client-server protocol – File manager part of client file system remains the same as that for the local file system • Only the file store is local or remote • Each remote file that is active manifests as an nfsnode in the client’s filesystem – Recall the active file data structures: • Per-Process File Descriptor – Kernel File Entry – vnode – file-store-specific data structure » inode for local file store and » nfsnode for remote filestore 11
- 12. BITS Pilani, Pilani Campus NFS - Operation • Basic Protocol (Mounting): Client C, Server S – C (mount process) -----> S(portmap daemon) • request port address of mountd – S (portmap daemon) ----> C • return the port address of its mountd – C (mount process) ----> S(mountd daemon) • request mounting of filesystem [pathname] – S (mountd daemon): • get file handle for desired mount point from kernel – S (mountd daemon) ---> C • return filehandle of mountpoint OR error 12
- 13. BITS Pilani, Pilani Campus NFS - Operation • Basic Protocol (I/O Operation): Client C, Server S – C (app. process): write system call • Data is copied into kernel buffer and call returns • nfsiod daemon wakes up – C (nfsiod daemon) -----> S(nfs_rcv) • Request write [buffer contents] – S delegates request to nfsd daemon • nfsd daemon invokes write on disk and waits for I/O – S (nfsd daemon) ---> C (nfsiod daemon) • return ack for the write operation 13
- 14. BITS Pilani, Pilani Campus NFSv3 vs NFSv4 • NFSv3 – One RPC per RTT – Port mapper service required to determine which network port to listen or connect – No caching • NFSv4 features – Access control lists (similar to Windows ACLs) – Compound RPCs – Client side caching – Operation over TCP port 2049 – Mandating Strong security (Kerberos v5 for cryptographic services) 14
- 15. BITS Pilani, Pilani Campus Thank You! 15