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• We recommend that you shut down Fedora 3 repository or put it into read-only mode, if you plan on migrating directly from Fedora 3 data on disk, to avoid issues of changes occurring while data is being written.
• When performing a sizable migration, run the utility in a screen or tmux session that you can detach from.  Try not to shut down or reboot the host while the tool is running.
• If the --working-dir isn't specified, the utility will use the current directory as the working directory, so an index directory and pid directory would be created in the current directory.
  • An index of the datastreams will automatically be created in <working_dir>/index, and then that index will be reused for future runs of the utility. If you need to update the index, or don't want it to be used for a new run of the utility, delete <working_dir>/index and the index will be re-created.
• If the migration is interrupted, you can pick up where the migration left off by relaunching the tool with the --resume flag (keeping all the other parameters the same).

• Redirect the output of the utility to a log file that you can analyze at your leisure during and after the migration.  Example:

  Code Block
  language bash title Redirect to log file
  java -jar migration-utils-6.0.0-driver.jar \ --source-type=legacy \ --target-dir=my-fcrepo-6-home \ --objects-dir=my-fcrepo-3/objects \ --datastreams-dir=my-fcrepo-3/datastreams > log.txt 2>&1

  
  

• Errors:  the migration tool may encounter problems copying some objects or datastreams.  The tool by default will halt at the first error;  if you wish to migrate as much as possible then go back and address errors, run the tool with the --continue-on-error flag.  Objects or datastreams with errors will not be written to the OCFL repository;  they will be skipped, and the next object in the list will be processed.
  Objects that could not be migrated will provoke a stack dump in the log, marked with the string ERROR.  They can be extracted from the log at a later date and fixed, then migrated individually.
  Example:

  Code Block
  language bash title Grep ERROR
  $ grep ERROR log.txt ERROR 01:09:09.801 (Migrator) MIGRATION_FAILURE: pid="test:BadPID1", message="Unable to resolve internal ID "test:BadPID1+MYDS+MYDS.2"!" ERROR 01:29:54.878 (Migrator) MIGRATION_FAILURE: pid="test:BadPID23", message="Unable to resolve internal ID "test:BadPID23+MYDS+MYDS.0"!" ERROR 02:11:50.644 (Migrator) MIGRATION_FAILURE: pid="test:BadPID617", message="Unable to resolve internal ID "test:BadPID617+MYDS+MYDS.1"!" ...

  
  

• Warning:  the migration utility is not idempotent!  This means that if you run the utility twice over the same content to the same target, you will wind up with an OCFL repository with duplicate versions of datastreamssee an exception when the utility tries to create an object that already exists.  For the purposes of testing, delete or move out of the way previous migration attempts before running a new migration.
  However, you can migrate new objects to an already-existing OCFL repository, which means you can plan your migration in stages, if you desire.  Note that you will need to rebuild your Fedora 6 index after the new additions.
• When adding new or fixed objects to the OCFL repository, make sure to regenerate a fresh datastream index.

• As many files are created per object and per datastream version, make sure to allocate enough inodes on your system to allow for all the files (note:  this should only be necessary for

  extremely large repositories, more than 4 million objects, for example).
• See Fedora 3 to 6 Migration Community Updates for examples of medium- and large-scale migrations performed with the migrations tool, with benchmark data and detailed notes.
• Warning: the migration can be run in multiple batches, by passing in a file containing a list of pids to migrate for each run. If you do this, make sure to remove pid/resume.txt once each batch is complete. Also, note that the utility still iterates over all the foxml files in your repository for each run, so you may notice some pauses where the utility is still running, but not logging anything.

Example migration workflow

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