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

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

Putting The Grandfather Method To Work

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Putting The Grandfather Method To Work
Restoring Files
Copyright © 2012-2017 by Matthew S Harris

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

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The Grandfather back-up method repeats a basic weekly cycle 12 times: Once each week (Friday), you make a full back-up. You make an incremental back-up each work day after that until the next Friday. (Do your back-ups at the end of the work day, preferably using the automatic scheduling features of your back-up application). This process creates a weekly "snapshot" of all the files, and a record of whatever daily file changes and creations occurred during the week.

When complete, the basic weekly cycle enables you to recreate the status of the backed-up files for any point in the preceding week - you restore all backed-up files from the full back-up to get the status you had at the start of the week, then restore the daily changes over the course of the week for as many days as you want or need.

The Grandfather method repeats this weekly cycle 3 times, each time using a different media set for the Friday backup — Friday 1 through Friday 3. On the fourth week (the last Friday of the month), you use one of the Month media sets for the Friday backup, thus completing a 4-week monthly cycle.

You repeat the 4-week monthly cycle 3 times, covering a total of 12-weeks.

Table 1 shows the rotation schedule for media sets for the full 12-week cycle. In the Grandfather back-up method, the week starts with each Friday's full back-up. The table indicates whether a specific back-up is full or incremental, and the name of the media set to use. If you need or want to include Saturdays and Sundays, simply insert an additional 2 daily incremental back-ups for those days.

As you can see in Table 1, you start the cycle (Week 1) on a Friday, using the Friday 1 full back-up media set. Each following week day — Monday through Thursday — you perform daily incremental back-ups.

Week 2 begins on the second Friday of the cycle. You perform a full back-up onto the Friday 2 media set, again followed by daily incremental backups. Week 3 is the same, except that you use the Friday 3 media set.

You start week 4 by using the Month 1 media set, followed (as every week) by your Monday through Thursday incremental back-ups.

With Week 5, you are starting the second month of the Grandfather back-up cycle. For Week 5 through Week 7, you perform the same weekly routine - a full back-up each Friday, rotating in order through the Friday 1, Friday 2, and Friday 3 media sets.

You start Week 8 by using the Month 2 media set. In Week 9 through 12, you perform the same 4-week cycle — rotating through the Friday 1-3 full backups, your daily incremental back-ups, and on the last week (Week 12) using the Month 3 media set for the final week.

At the end of Week 12, you have backed up 12 weeks of data, and are ready to start the cycle again. Continue performing incremental daily back-ups and full back-ups on each Friday, using the Friday 1, Friday 2, and Friday 3 media sets in order. Every 4 weeks, use the Month 1, Month 2, and Month 3 media sets in order. As long as you continue this cycle, you can use your backed-up files to recover all your backed-up data or individual files and folders from the past three months.

Table 2 in "Restoring Files" shows this same 12-week rotation in a calendar grid for the actual dates December 31, 2010 through March 24, 2011.

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