AFS

1. Cell Name in DESY Zeuthen
2. AFS Home Directories in DESY Zeuthen
3. AFS Backup/Recover at DESY Zeuthen
4. acrontab
5. Usage of storage locations
6. AFS Usage Hints
7. Documentation to AFS

1. Cell Name in DESY Zeuthen

The DESY Zeuthen cell name is ifh.de

2. AFS Home Directories

All users have an AFS home directory. A user with account name testuser has the following AFS Home Directory: /afs/ifh.de/user/t/testuser/
You can have up to 2 Gigabyte quota. Please contact uco-zn@desy.de for increasing.

To have an AFS home directory has a lot of advantages:

  • better support for setting permissions
  • this home is available at DESY Hamburg, CERN and other sites which support AFS


There are some things to know:

  • AFS file access control is by directory, but more flexible and done with fs setacl instead of chmod.
  • Although Unix file access rights are still visible, most will be ignored by AFS.


An AFS token is needed to access anything in AFS that's not (literally!) world-readable. This AFS token has a lifetime of about 25 hours. You get this during the normal login, using kinit. A screensaver activated your xsession. With klist or tokens you can see the current tickets/tokens.

Hence there are some inconveniences when you want processes of yours to run unattended (cron- or background- jobs):
If they need access to your home directory (which is sometimes hard to avoid), they need a valid AFS token. Facilities like acrontab and the Batch System take care of that.

3. AFS Backup/Recover at DESY Zeuthen

Information about recover of complete volumes and individual files or directories.

4. acrontab

The acrontab command allows scheduling of cron jobs with valid AFS tokens.

5. Usage of storage locations

Purpose

Path

Persistence

Backup Strategy

Visibility

Remarks

valuable user data

/afs/ifh.de/user/
<initial>/<user>

permanent

automatic, daily backup

on all machines

contact: uco-zn@desy.de

group data

/afs/ifh.de/group/

permanent

backup for all AFS volumes names of which start with g., but not gn.

on all machines

contact: your group AFS admin
See: AFS Backup

small data, easy to reproduce

/afs/ifh.de/group/

nearly permanent

no backup

on all machines

contact: your group AFS admin

6. AFS Usage Hints

  • distribute large datasets over a number of volumes
  • volumes should not be larger than a few dozen GBytes (moving to a different server possible, selective replication possible, higher throughput if datasets distributed over servers, minimize risk)
  • ask your AFS group admin to distribute the volumes to different servers in case of heavy usage within batch
  • in case of heavy read actions within batch your AFS group admin should create read-only replicas of your volumes on different servers for better throughput
  • please do not move gigabytes of data from one AFS location to another, instead, mount volumes under different paths
  • AFS drawbacks
    • there's a limit of <~ 64k entries per directory (for short filenames; for longer names it's 32k or lower)
    • slow client, local cache is a burden on the client especially for large files
    • ACLs are per directory, not per file
    • need special solutions for cron job (if write access required, or read access to private data), use acrontab

7. Documentation to AFS


Top