(A short version of this article first appeared in Matthew Harris' Disk Compression Book)

The "Grandfather-Father-Son" Back-Up Method

Restoring Files

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Restoring Files
Copyright © 2012-2017 by Matthew S Harris

Matthew S Harris is a software & database designer, contract programmer & consultant.

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Restoring a file (or folder) means retrieving it from your back-up media sets. The two main situations under which you will find it necessary to restore files are:

The next two sections describe how to restore files for each of the situations just described.

Recover From Complete Data Loss

To recover from a complete loss of your data, you need to restore the most recent version of all of your backed-up files. This task is easy and straightforward:

  1. Restore all files from the most recent full back-up.
  2. Restore all files from each of the daily incremental back-ups (Monday, Tuesday, Wednesday, Thursday) in order until you reach the last, most recent day of back-up.

Performing these two steps restores the status of the backed-up files up to the day before the actual data loss.

As an example of how to recover from a complete data loss, assume that you have started a Grandfather method back-up on December 31, 2010 (which conveniently falls on a Friday, refer to Table 2). You proceed through the back-up cycle described in "Putting The Grandfather Method To Work". On Wednesday, March 16th, in the 11th week of the cycle, you experience a total data loss.

To recover your data, you first restore all of the files from the most recent full back-up, in this case from the media set Friday 3, containing a full back-up made on March 11th (refer to Table 2).

Next, you restore, in order, all of the files from your daily incremental back-ups from Monday (March 14) and Tuesday (March 15). The data loss occurred on Wednesday the 16th, so you do not need to restore from the Wednesday or Thursday media sets.

Your files are now restored to their status as of the time of Tuesday's back-up, and the only data permanently lost is whatever changes occurred between the time of that back-up and the time of the actual data loss.

Recover Deleted or Corrupted Files

Occasionally, files or entire folders are accidentally deleted, and may not be recoverable from your operating system's "trash bin". Other times, a file's contents may be accidentally deleted, or the file may become corrupted and unusable. A properly implemented Grandfather back-up, especially one done at maximum thoroughness (see "How Thorough?"), enables you to restore individual files and folders to recover the most recent intact versions.

Restoring from a Thorough Back-up Set

If you have implemented the Grandfather method at maximum thoroughness, you can restore single files or entire folders:

As an example of restoring an entire folder, assume that you notice on Tuesday, February 8th (refer to Table 2) that a folder named \Task13 is missing as the result of an accidental deletion. To restore this folder, you start looking for it in the full back-up made on February 4th (in the media set labeled Friday 2). If the \Task13 folder is not present in this back-up, you look next in the previous full back-up performed on January 28th (Friday 1). If you still can't locate the folder, you continue looking in the next previous full back-up of January 21 (from the Month 1 media set).

Assuming you do find the \Task13 folder in the full back-up of January 21, you restore the folder from this backup. Next, you check the Monday incremental backup of January 24th (refer to Table 2), for any files backed-up from the \Task13 folder. If there are files from the \Task13 folder on the incremental back-up, restore them. Repeat this task for each daily incremental back-up for that week only. The next full-backup does not contain the \Task13 folder, so you know that the folder disappeared sometime during the preceding week. As you have, at this point, restored the last available complete copy, plus the week's worth of incremental changes, you are done restoring the \Task13 folder.

Restoring from a Media-Saving Back-up Set

If you have implemented the Grandfather method to save media, you can still recover single files and folders.

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