Candidate selection for automatic migration

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Files in a file system, which become eligible for automatic migration, are considered candidates for automatic migration. The dsmscoutd daemon finds the best candidates for automatic migration. It also prioritizes the files based on the file age, the number of days since a file was last accessed, and the file size.

For a file to be eligible for automatic migration, it must meet these requirements:
  • Be in a file system to which space management was added
  • Meet all management class requirements for eligibility
  • Meet the minimum required size for migration
  • Be included for space management services

When a file system is added to space management, the dsmscoutd daemon creates a complete file index (CFI) in the .SpaceMan/metadata directory for the managed file system. The CFI requires space equivalent to 1% to 3% of the managed file system. If the CFI is not created, view the dsmerror.log file for more information and use the dsmscoutd scanplan command to obtain additional information.

When a file system is removed from space management, the CFI is removed.

The CFI is updated by various processes:
  • The daemon periodically scans the managed file systems and updates the CFI with the latest information about every file. The information is used to generate a list of files that is used for threshold and demand migration. Before migration, each file is checked to determine whether it is still eligible for migration.
  • The dsmrecall and dsmmigrate commands update the CFI. When a file is restored as a migrated file, the file information is stored in the CFI.
The following commands and options can modify or monitor automatic migration:
  • The minmigfilesize option in the dsm.sys file. Specify the minimum file size for a file to be eligible for automatic migration.
  • The dsmscoutd scanplan command. Monitor the next scan time or the remaining time before the next scan for one or more managed file systems.
  • The maxcandprocs option in the dsm.sys file. Change the number of scans that can run in parallel in the daemon.
  • The maxcandidates parameter of the dsmmigfs command. Improve the performance of automatic migration by lowering the value to 100.
    Note: Do not increase the value of maxcandidates higher than 1000. A higher value slows down the automatic migration. For best results on your system, select a value from 10 - 500. The optimal number to use depends on the performance of the file system and operating system.

On IBM® Storage Scale file systems, you can use the IBM Storage Scale policy engine to monitor space thresholds and search for migration candidates. In this case, the space monitor and scout daemons are disabled.

For information about configuring IBM Storage Scale integration with the space management client, see Technote 7018848.