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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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13.4.1 File naming<br />

DFS follows the client/server model, <strong>and</strong> it extends the concept of DCE cells by<br />

providing DFS administrative domains, which are an administratively<br />

independent collection of DFS server <strong>and</strong> client systems within a DCE cell.<br />

There can be many DFS file servers in a cell. Each DFS file server runs the file<br />

exporter service that makes files available to DFS clients. The file exporter is<br />

also known as the protocol exporter. DFS clients run the cache manager, which<br />

is an intermediary between applications that request files from DFS servers. The<br />

cache manager translates file requests into RPCs to the file exporter on the file<br />

server system <strong>and</strong> stores (caches) file data on disk or in memory to minimize<br />

server accesses. It also ensures that the client always has an up-to-date copy of<br />

a file.<br />

The DFS file server can serve two different types of file systems:<br />

► Local file system (LFS), also known as the episode file system<br />

► Some other file system, such as the UNIX File System (UFS)<br />

Full DFS functionality is only available with LFS <strong>and</strong> includes:<br />

► High performance<br />

► Log-based, fast restarting file sets for quick recovery from failure<br />

► High availability with replication, automatic updates, <strong>and</strong> automatic bypassing<br />

of failed file server<br />

► Strong security with integration to the DCE security service providing ACL<br />

authorization control<br />

DFS uses the Cell Directory Service (CDS) name /.:/fs as a junction to its<br />

self-administered namespace. DFS objects of a cell (files <strong>and</strong> directories) build a<br />

file system tree rooted in /.:/fs of every cell. Directories <strong>and</strong> files can be accessed<br />

by users anywhere in the network using the same file or directory names, no<br />

matter where they are physically located, because all DCE resources are part of<br />

a global namespace.<br />

As an example of DFS file naming, to access a particular file from within a cell, a<br />

user might use the following name:<br />

/.:/fs/usr/woodd/games/tictactoe.exe<br />

From outside the cell, using GDS (X.500) format, the following name is used:<br />

/.../C=US/O=<strong>IBM</strong>/OU=ITSC/fs/usr/woodd/games/tictactoe.exe<br />

510 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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