Scratch Space Described

Scratch space is temporary storage for files.  Most of the time you will want to use your own permanent storage but there are situations where scratch might be more appropriate.  For example,

  • You are doing a computation that requires large amounts of temporary space but only while the computation is running.
  • You have a data set larger than what you can fit into your own permanent storage but you only need it for a short period of time (e.g. a month).
  • You are doing a computation that needs higher performance storage than what your own permanent storage can provide.

Scratch policies

  • Don’t write directly to the top level of a scratch volume. Instead create a sub-directory that matches your username. For example “mkdir /scratch/mynetid” if you login with your netid and want to use the /scratch volume on one of our systems.
  • Files and directories older than 45 days in scratch are automatically purged because this is a shared and limited resource.
  • One week before any of your files are deleted you will receive a warning email. When possible, we include a list of those files. This is your opportunity to request an extension for files whose usefulness has gone on longer than expected.
  • We cannot make any guarantees about the safety of data in scratch volumes. It’s intended to be temporary and safety is traded off for performance. There are no backups and many of these volumes are arrays of disks where failure of one disk means the loss of all data in the volume.

Characteristics of specific scratch volumes

discovery:/dartfs-hpc/scratch

  • network storage, available to entire Discovery cluster
  • exact same performance as anything else mounted from /dartfs-hpc (e.g. home directories and Tier 3 lab directories)
  • not subject to individual drive failures

discovery&computenode:/scratch

  • local to that machine
  • usually somewhat less performance than /dartfs-hpc/scratch but not subject to network slowdowns
  • subject to individual drive failure

polaris:/scratch

  • local to Polaris
  • an extremely fast array of drives
  • excellent for streaming reads/writes
  • subject to individual drive failure

andes:/scratch

  • local to Andes
  • an extremely fast array of drives
  • excellent for streaming reads/writes
  • subject to individual drive failure

polaris&andes:/scratch-nfs

  • network storage, available to both Polaris and Andes
  • same performance as /dartfs-hpc/scratch on Discovery
  • not subject to individual drive failure