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Scratch Dir


This start-up directive allows the user to specify the directory location of scratch files created by NWChem. NWChem distinguishes between permanent (or persistent) files and scratch (or temporary) files, and allows the user the option of putting them in different locations. In most installations, however, permanent and scratch files are all written to the current directory by default. What constitutes “local” disk space may also differ from machine to machine.

The conventions for file storage are at the discretion of the specific installation, and are quite likely to be different on different machines. When assigning locations for permanent and scratch files, the user must be cognizant of the characteristics of the installation on a particular platform. To consider just a few examples, on clusters, machine-specific or process-specific names must be supplied for both local and shared file systems, while on SMPs it is useful to specify scratch file directories with automated striping across processors with round-robin allocation. On SMP clusters (a.k.a. constellations), both of these specifications are required.

The SCRATCH_DIR enables the user to specify a single directory for all processes or different directories for different processes. The general form of the directive is as follows:

(SCRATCH_DIR) [(<string host>||<integer process>):]  <string directory>  [...]

Directories are extracted from the user input by executing the following steps, in sequence:

  1. Look for a directory qualified by the process ID number of the invoking process. Processes are numbered from zero. Else,
  2. If there is a list of directories qualified by the name of the host machineAs returned by util_hostname() which maps to the output of the command hostname on Unix workstations., then use round-robin allocation from the list for processes executing on the given host. Else,
  3. If there is a list of directories unqualified by any hostname or process ID, then use round-robin allocation from this list.

If directory allocation directive(s) are not specified in the input file, or if no match is found to the directory names specified by input using these directives, then the steps above are executed using the installation-specific defaults. If the code cannot find a valid directory name based on the input specified in either the directive(s) or the system defaults, files are automatically written to the current working directory (“.”).

The following is a list of examples of specific allocations of scratch directory locations:

  • Put scratch files from all processes in the local scratch directory (Warning: the definition of “local scratch directory” may change from machine to machine):

scratch_dir /localscratch

  • Put scratch files from Process 0 in /piofs/rjh, but put all other scratch files in /scratch:

scratch_dir /scratch 0:/piofs/rjh

  • Put scratch files from Process 0 in directory scr1, those from Process 1 in scr2, and so forth, in a round-robin fashion, using the given list of directories:

scratch_dir /scr1 /scr2 /scr3 /scr4 /scr5

  • Allocate files in a round-robin fashion from host-specific lists for processes distributed across two SGI multi-processor machines (node names coho and bohr):

scratch_dir coho:/xfs1/rjh coho:/xfs2/rjh coho:/xfs3/rjh  bohr:/disk01/rjh bohr:/disk02/rjh bohr:/disk13/rjh