Andrew File SystemCSS534

ZACH MA

History Originated in October 1982, by the Information Technology Center (ITC) formed with Carnegie Mellon and IBM Corporation

Commercialized by Transarc Corporation in 1989 and then made into an IBM product that was extensively used in the 1990s.

Made open-source by IBM under the name OpenAFS in 2000, and continues to be in widespread use at Carnegie Mellon and many other institutions.

General Goals High availability

Ease of expansion

Incorporation of new technologies

Good performance even during peak periods

With graceful response to overload

Design Choices Make the file system compatible with UNIX at the system call level

Use whole files as the basic unit of data movement and storage, rather than some smaller unit such as physical or logical records

Implement it with many relatively small servers rather than a single large machine

Servers and Clients Two basic classes of machines

File server machines

Client machines

File server machines provide file storage and delivery service, along with other specialized

services, to the other subset of machines in the network, the client machines

There are generally many more client workstations than file server machines.

Server Processes File Server

Basic OverSeer Server(BOS Server)

Protection Server

Volume Server

Volume Location Server(VL Server)

Salvager

Update Server

Backup Server

File Server Delivering and storing files

Maintaining the hierarchical directory structure

Handling all types of file requests

Keeping track of status information

Validating user identity

Creating symbolic and hard links between files

Basic OverSeer Server(BOS Server) Constant monitoring on the other server processes

Automatic incident response

Interacting with system administrator

Helps system administrators to manage system configuration information

Client Processes – Cache Manager Only component that resides on client machines

Main duty is to translate file requests (made by application programs on client machines) into

remote procedure calls (RPCs) to the File Server.

Cache files before passing data on to the application program

Track the state of files

Cells and Volumes Cell

A cell is an administratively independent site running AFS.

Volume

A unit of disk space that functions like a container for a set of related files, keeping them all

together on one partition.

Can vary in size, but smaller than a partition.

Other Parts Required Kerberos KDC (Key Distribution Center)

Performs two main functions related to network security

Verifying the identity of users

Providing methods to achieve mutual authentication

Network Time Protocol Daemon(NTPD)

Guarantee that all of the file server machines and client machines agree on the time

VL Server Interaction

Password and Mutual Authentication

Updating Copies of Cached Files

X

X

->Y

->Y

->Z

->Z

Summary Pros:

Scalability

Security

Reliability

Availability

Cons:

Authentication may cause problems

Conflicts with UNIX file semantics

References [1] Howard, John H. An overview of the andrew file system. Carnegie Mellon University,

Information Technology Center, 1988.

[2] Administrator Guide, http://docs.openafs.org/index.html

[3] User Guide, http://docs.openafs.org/index.html

[4] http://en.wikipedia.org/wiki/Andrew_File_System

[6] http://www.cmu.edu/corporate/news/2007/features/andrew/history_overview.shtml