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Note - As of July 1st, 2016, files on scratch filesystems are subject to deletion 60 days after they were created.

User Scratch Space

Each compute node has its own local scratch filesystem. Users may read from and write to this using their own exclusive directory at /localscratch/Users/<HawkID>.

In addition to local storage, each HPC cluster has its own large, shared filesystem mounted across all its nodes via NFS. Analogously, users can read from and write to this using their own exclusive directory at /nfsscratch/Users/<HawkID>.

Cleanup Policy

Scratch filesystems are a shared resource available for the convenience of all users. Therefore, files on these filesystems are subject to deletion after a certain lifespan as determined by the HPC policy committee. Home account storage and purchased storage are not subject to this policy.

/localscratch

On /localscratch, the allowed file lifespan is 30 days after the file was last accessed, and a file's age is the time elapsed since its access timestamp ("atime"). An automated cleanup process will run periodically on each node to delete files whose atime has reached the maximum lifespan. It is also expected that large amounts of data put on /localscratch are cleaned up at the end of a job. Otherwise, the node become unavailable. A node left in this condition will have /localscratch clean entirely, irrespective of time stamps, to make the node available again.

/nfsscratch

On /nfsscratch, the allowed file lifespan is 60 days after first being written to an /nfsscratch filesystem, and a file's age is the time elapsed since its creation timestamp ("crtime") which is tracked on the fileserver. An automated cleanup process will run periodically on the server to delete files whose crtime has reached the maximum lifespan.

Altering or duplicating files solely to circumvent the scratch cleanup process is against policy. Please make legitimate use of scratch filesystems, then move your intermediate and final results to stable storage in accordance with policy.

Please contact hpc-sysadmins@iowa.uiowa.edu with any questions or for assistance with this.

Local or Shared Scratch?

  • Multiple jobs might be running on your job's node. These jobs can compete for local storage I/O, causing contention independent of /nfsscratch. Only a job with exclusive access to a node can expect the full performance potential of the node's local storage.
  • A parallel job running on multiple nodes typically shouldn't use filesystems local to any of its nodes. Even if you're writing your own MPI instead of using an off-the-shelf application, you can expect better performance if you collate results in memory via message passing and write your result to the shared filesystem. Consider local disk primarily as a structured alternative to swap.
  • If your job places partial results on /localscratch but fails to handle them for any reason (logic error, eviction, crash, etc.), you won't have access to these anywhere else and they will be difficult to recover.
  • As always, please test a few jobs if you are unsure.

File Timestamps

  • modification time (mtime): This is the time the contents of the file were last modified, for example, by editing it. The modification time can be seen with
    ls -l file
  • change time (ctime): This is the time the metadata of the file was last changed. An example of this would be moving a file to a different directory. The change time can be seen with
    ls -lc file
  • access time (atime): This is the time the contents of the file were last accessed; for example, by viewing with 'less'. The access time can be seen with
    ls -lu file
  • creation time (crtime): This is the time the contents of the file were first written to the filesystem. This attribute is part of the underlying ZFS filesystem and is not accessible via NFS or standard Linux utilities.

All of these timestamps can be different for a single file. Most file and archive utilities will maintain the first 3 timestamps, either by default or optionally. This includes using archive mode ('-a') with either 'cp' or 'rsync'. However, note that no utility can affect a file's crtime at all over NFS.

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