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Incremental backup

Project description

A Python class for file comparison and new file backup.

Author: Yu Sun at University of Sydney

Email: sunyu0410@gmail.com

Website: https://github.com/sunyu0410/AmendmentBackUp

Motivation

When it comes to backing up a large amout of data, it is often preferable to only copy the modified and unique files, rather than simply coping the whole directory. The AmendmentBackUp (ABU) class provides a simple interface to do that. No dependencies are required apart from the Python 3 standard library.

Design

Say we have two folders, a source folder dir1 which you have your most recent files and a reference folder dir2 which holds some of your previous backup. What the ABU does is to compare all files in dir1 with those in dir2, and copy the files to a third destination folder dst. If you simply want to add the files to the original back, you can set dst to dir2.

A quick example

from AmendmentBackUp import *
createDemo()
abu = AmendmentBackUp(dir1=r"demo/dir1",
                      dir2=r"demo/dir2",
                      dst=r"demo/dst")
abu.compare()
abu.backup()

Explanation

Say you have the dir1 and dir2 with the following tree structures:

dir1 (source, recently updated)
|   file1.txt
|   file2.txt (modified)
|   file3.txt (unique)
|
+---subfolder1
|       file4.txt
|
+---subfolder2
|       file5.txt
|       file6.txt (modified)
|
\---subfolder3 (unique)
        anyfile.txt

dir2 (reference, previous backup)
|   file1.txt
|   file2.txt
|   file7.txt
|
+---subfolder1
|       file4.txt
|
\---subfolder2
        file5.txt
        file6.txt

dst (destination)

You can inititate an ABU object by calling

abu = AmendmentBackUp(dir1=r'demo/dir1',
                      dir2=r'demo/dir2',
                      dst=r'demo/dst')

By the way, the createDemo() will create the demo file structures shown above.

After initiation, what ABU will do:

  • Comparison (abu.compare()) by walking through all files and folders in dir1 and check the existence of the corresponding counter in dir2.

    • If no, then add to the copy list. For folders, this will be the entire folder.

    • If yes, compare the two folders (shallow comparison using the time stamp and the file size) for files;

      • If the comparison returns False, add to the copy list;

      • Otherwise, continue to the next one.

  • Copy (abu.backup()) the files and folders in the copy list.

    • Folders will be copied first. If the parent folder has been copied, any child folder will be skipped;

    • Files will copied next. If the file falls under any folder from the previous step, it will be skipped.

  • The meta data of the backup process will be store in a folder called _abu with a time stamp (year-month-day-hour-minute-second) in the dst folder. These include

- abu_log.txt      Log file
- abu_obj.pickle   ABU object of this backup task
- dir1_tree.txt    Tree structure of dir1 (source)
- dir2_tree.txt    Tree structure of dir2 (reference)
- dst_tree.txt     Tree structure of dst (destination)

Limitation

The ABU is best suited when the source folder dir1 is a natural growth of the reference folder dir2. What natural growth means is that there should not be too much renaming or move of the subfolders from dir2 to dir1. Otherwise, using a version control system is probably a better option since ABU won’t track the history of any folder or file.

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