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Mu2e AFS Disk Space

What is AFS?

Fermilab uses a distributed networked file system, the Andrew File System (AFS), to share disk space among many computers both at Fermilab and off-site; these disks are even mounted at CERN and in Asia. The short description is that AFS works much like NFS but it is optimized under the assumption that computers may be connected by a slow network: so timeouts are longer and there is a different optimization of the local caching policy.

Mu2e AFS Spaces

/afs/*/<your_kerberos_principal>     Your home area on GPCF and FNALU but not on detsim.
/afs/* Obsolete: an old Mu2e code area.
/afs/* Obsolete: an old Mu2e data area. Not backed up!

Normally you should not use the data and code areas mentioned above. Instead you should use the blue-arc disk resources.

Both the home areas and the code areas are backed up nightly. The reason for the many d* areas is that each is limited to a maximum capacity of 8 GB ( this value was originally limited by the size of available backup media; it now just is).

AFS Access Control

In AFS space the usual unix file permissions are ignored. Instead control is governed by Access Control Lists (ACLS). The following command will show the list of users and user groups who are allowed to access the AFS space at the given path:
> fs listacl /afs/
One of the allowed user groups is rhbob:mu2e. To see who is in this group:
> pts members rhbob:mu2e
For additional information follow the links above to the AFS documentation.

To be added to the ACLs that grant access to the Mu2e data and code disks, send email to

AFS Can be Slow

AFS is tuned to share disk space among nodes that are connected by a wide area network, not just by a local area network; that is, it is able to deal with response times between nodes that are on different continents. A side effect of this is that sometimes AFS has a slow response, even if you are accessing disk that is actually on a local network. Sometimes it can take a few seconds to get the output of an ls command or to open or close a file. For this reason, afs is not mounted on detsim.

Mounting AFS on your Desktop or Laptop

One handy way to get access to Mu2e code and data files is to mount the Mu2e AFS space on your desktop, laptop or on a cluster of computers at your home institution. However, because AFS can be slow, and because disk space is relatively cheap, it will often make more sense to make a copy of the material in AFS space on your machine(s).

Still to come:

Ownership Details

The Mu2e code and data afs spaces are owned by the user rhbob (Bob Bernstein) who is the only administrator with full powers. Access to these disk spaces is controlled via two user groups:

To Do List

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This file last modified Friday, 20-Nov-2015 15:02:49 CST
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