What is AFS Land?

by Dr. Alex Yu

The Andrews File System (AFS) is a distributed file system with a common name space. Before I explain AFS, first you should learn what a file system is. A file system is for an operating system to organize and keep track of files. Common file systems are:

Platform File System
DOS/Windows 3x/Windows 95 16-bit File Allocation System (FAT16)
Windows 98 32-bit File Allocation System (FAT32) (gain weight?)
Windows NT New Technology File System (NTFS)
Linux EXT2
Mac 8.0 or lower Hierarchical File System (HFS)
Mac 8.1 or higher Extended Hierarchical File System (HFS+)
OS/2 High Performance File System (HPFS)

The list can go on and on. Some people may scream, "What! I thought all PCs are the same and so are all Macs. How come there are three file systems in Windows computers and two in Macs?" Welcome to the world of diversity. This is the spirit of America! The bad news is: Different file systems store files differently. For example, files stored in Windows NT's NTFS partition cannot be read by Windows 98, which uses FAT32, and vice versa. The good news is: AFS is a universal file system. Although in your organization there may be different file servers, with AFS all the files can be accessed by one set of login name and password, and therefore the user has an illusion that their files are stored in one place. Actually, user files are stored in different volumes on AFS file server machines and accessed through a cache manager on AFS clients. If you are curious about where your file is, invoke the following command:

% fs whereis <dir/file path>

This file system is named the Andrews File System because it was introduced at Carnegie-Mellon University (CMU) and the last name of Carnegie is Andrews. Some computer experts predicted that in the future AFS would be expanded to a global distributed file system and sooner or later file transfer protocol (FTP) would become obsolete. However, currently AFS is still NOT a global file system yet and therefore users are advised to stay with FTP.

The basic unit of AFS is a cell, which is equivalent to a directory in PC and a folder in Macintosh. A cell organizes and maintains its own space. Also it can connect to other local or remote cells running AFS.

In PCs and Macs the cache memory can help to speed up the processing by storing the most frequently used commands and files in the memory. A server can also use cache to "read ahead" and "write behind." i.e. instead of doing input-output whenever the user alters the file, the server stores many changes in the memory and then writes the file at one time. AFS adopts the same strategy. In AFS permanent are made only when the file is closed or saved.

When you log into a UNIX server, you may see your quota information as the following:

If you cannot see the above information, use the following commands:

% fs listquota

The percentage of used space is the amount of space owned by you. AFS is a space sharing system. The percentage of partition indicates the amount of space used by yourself and other users.

AFS commands are NOT UNIX commands. There are many advanced techniques in AFS for users to share files with others. If someday you see AFS emerging and FTP going down, perhaps you should make efforts to learn more about AFS.
You can access AFS Land from a Mac with an ethernet connection if you have an AppleVolumes in your UNIX account. To check if you have Apple Volume, type ls at the UNIX prompt to list all your files. If you don't have an AppleVolumes, do the following (This setup is in the system of Arizona State University. The setup procedure may vary from system to system):

  1. Login your UNIX account, at the shell type pico AppleVolumes.

  2. A blank file will appear. Add the following lines into the document. The last two lines are universal, but the first one depends on your user name.

    afs/.asu.edu/users/(the first letter of my user name)/(the second letter)/(the third letter)/(full user name)

    /afs/asu.edu

    /afs/asu.edu/mac

    For example, my user name is alexyu and therefore my first line is:

    /afs/.asu.edu/users/a/l/e/alexyu

  3. After you've finished editing, press Control-X at the same time to save your file.

Once it is setup, you can access your AFS Space from the Mac Chooser as the following:

1. Open Chooser from AppleMenu.

2. A dialog box will pop up, choose AppleShare from the upper left box, IT CC Atrium from the lower left box, then AFS Land from the upper right box. Afterwards, click OK.

3. Login on by using your UNIX account ID and password.

4. Select your user name, then click OK. Do not check the square box otherwise next time the Mac will start up with your AppleVolumes.

5. Now you have an AppleVolumes on your desktop. You may transfer your files by dragging and dropping.