Our user-data is stored in /users on psilodump on an ISCSI volume exported to aspartame, which exports /users/ via NFS. Plans to add a layer of LVM abstraction so as to support regular snapshot backups of /users/ are currently in-place, but not yet fully implemented. All of our systems NFS mount /users, and most of them do so using Kerberos for authentication.
We have also explored additional methods for replicating user-data, including AFS, Coda, and DRBD, but have found all to be unusable or problematic.
NFSv3 has been in long standing use by the CSC as well as almost everyone else on the planet. NFSv4 mounts of /users are currently in the works to CSCF. Unfortunately NFS has a number of problems. Clients become desperately unhappy when disconnected from the NFS server. Also previous to NFSv4 there was no way to client side cache, resulting in poor performance with large files.
On November 8, 2007, we experienced a major NFS failure. An analysis of the logs indicated that the fault was likely caused by NFSv4-specific code. As a result, we have returned to mounting with NFSv3.
On March 15, 2008, we transitioned to ZFS. This move has since been reversed; details are preserved in a previous revision of this page