Carnegie Mellon University School of Computer Science

AFS in SCS

The Andrew File System (AFS) was developed here at Carnegie Mellon University as part of the Andrew Project and is named after Andrew Carnegie and Andrew Mellon.

AFS is a distributed client/server system that provides most SCS file-sharing services. SCS user accounts each have 1 GB of AFS space, and "Facilitized" Unix/Linux and Windows hosts include AFS clients.

The AFS system provides:

  • Transparent access to files — AFS files may reside on different servers but are accessed in the same way as files on your local disk, regardless of their actual physical location
  • A uni namespace — A given AFS file has exactly the same pathname on any Unix host
  • Secure, fine-grained access control — File owners can specify precisely which users have access to AFS files and what rights they have

AFS Concepts and Terminology

Cells
AFS, at the top level, is organized into AFS Cells, which correspond to separate administrative groups. SCS Computing Facilities administers the cs.cmu.edu cell, and there are other AFS cells on campus. 

AFS Cells and Cross-Realm Authentication

Volumes & Quotas
Related directories in AFS are organized into units called volumes, each with its own quota that determines how much disk space it can use. For example, a user's personal home directory, typically /afs/cs.cmu.edu/user/<user_ID>, will live in its own AFS volume. 

AFS Academic Volumes

AFS Project Volumes

AFS User Volumes


File permissions and ACLs
AFS does not use standard Unix permissions to protect files but, instead, attaches an Access Control Lists (ACL) to each AFS directory (not each file) and controls most access according to the ACL constraints.

AFS Permissions (Access Control Lists)

Authentication
Within SCS, AFS access is based on secure, limited-lifetime, tokens that you obtain when you login using your SCS Kerberos password or when you run kinit.

AFS Authentication 

Backup & restore
SCS Facilities backs up most AFS volumes automatically. See the AFS Backups page for details.

AFS Backup and Restore