TCP IP Illustrated

5 it can take the nfs server a while to handle a

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: file. The kernel determines this when the file is opened. After the tile is opened, the kernel passes all references to local tiles to the box labeled "local file access," and all references to an NFS tile are passed to the "NFS client" box. 2. The NFS client sends RPC requests to the NFS server through its TCP/IP module. NFS is used predominantly with UDP, but newer implementations can also use TCP. 3. The NFS server receives client requests as UDP datagrams on port 2049. Although NFS could be made to use the port mapper, allowing the server to use an ephemeral port, UDP port 2049 is hardcoded into most implementations. 4. When the NFS server receives a client request, the requests are passed to its local file access routines, which access a local disk on the server. 5. It can take the NFS server a while to handle a client's request. The local file-system is normally accessed, which can take some time. During this time, the server does not want to block other client requests from being serviced. To handle this, most NFS servers are multithreaded-that is, there are really multiple NFS servers running inside the server kernel. How this is handled depends on the operating system. Since most Unix kernels are not multithreaded, a common technique is to start multiple instances of a user process (often called nfsd) that performs a single system call and remains inside the kernel as a kernel process. 6. Similarly, it can take the NFS client a while to handle a request from a user process on the client host. An RPC is issued to the server host, and the reply is waited for. To provide more concurrency to the user processes on the client host that are using NFS, there are normally multiple NFS clients running inside the client kernel. Again, the implementation depends on the operating system. Unix systems often use a technique similar to the NFS server technique: a user process named biod file:///D|/Documents%20and%20Settings/bigini/Docu...homenet2run/tcpip/tcp-ip-illustrated/nfs_netw.htm (8 of 23) [12...
View Full Document

Ask a homework question - tutors are online