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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
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...
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- Spring '12