Page History

...

• Please do not store under the scratch folder data that you cannot recreate because this directory is not backed up and the oldest files on scratch may be deleted at any time to make space for data from new experiments.
• For files in scratch/, results/ and calib/ the age is determined using last modification time of a file (not access time).
  For the xtc and hdf5 files the access time is used (see  xtc/hdf5 cleanup).
  
• The tape archive (xtc, hdf5, usrdaq) and the tape backup (results, home) are fundamentally different:
  • In the tape archive the folders are frozen after the end of the experiments and their contents are stored on tape once. 
  • In the tape backup, the system takes snapshots of the folders as appear at a given time. This implies that files which are deleted from disk are eventually, i.e. after a long enough time, also deleted from tape. 
• Files under xtc and hdf5 can be restored from tape using the file manager tab in the electronic logbook. Files under home can be restored by the user following the instructions below.  To restore data from results send an email to cdspcds-datamgt-l@slac.stanford.edu.
• For raw data the cleanup operations will affect all files, i.e. all streams and chunks, which make up one run, rather than individual files.
• After 2 years from the end of an experiment we'll remove the experiment from disk. At that point we'll take a snapshot of the results and calib folders and archive them to tape so that we can, upon request, restore an entire experiment back to disk.
• After 10 years we plan to remove the tapes with the archived raw data from the silos and store them in a safe environment.
• The new policy will apply to all experiments, i.e. it will be retroactive, and its deployment date will coincide with the start of Run 14 (August 10^th 2016).
• For questions regrading the data retention and data access send your question to: pcds-datamgt-l@slac.stanford.edu.

...

The purging thresholds might vary depending on the size of a file system and its usage but typically are 5% and 10% (minimum/maximum threshold).  Using these three rules we try to keep runs that are actively analysed for as long as possible on disk and providing sufficient disk space for the ongoing experiment.

Restore of files

The xtc and hdf files are archived to tape and can be restored to disk in case runs were purged from disk. Restores are requested using the FileManager of the experiments eLog. A basic guide to the UI is described in  Managing Files.

The requests are sent to a queue which is monitored by a process that will retrieve the files from tape. The restore time might vary from tens of minutes to many days depending on the amount of data to be restored but also how busy the tape system is. In particular if high throughput experiments are running the restore will take a backseat. 

Rationale for Proposed Policy

...