Getting a better handle on GFS (Grandfather-Father-Son) backups

Posted on 2013-11-04
Last Modified: 2016-10-27
Call this an extremely newbie question but my question is on the use of a GFS backup strategy for data.  What I need to wrap my head around is what and from what time data can be recovered from.  Specifically from this example:  If I backup a file server with a weekly full, daily incremental and a monthly full, no matter the software and I retain every daily for one week, 4 weeks for the monthly and a single monthly and retain these for 3 years.  I would in effect have 12 backups at the end of each year (not after 3 years and if the software did a yearly you would have one backup for each year, 3 yearly tapes).  So now comes along a user who says they remember a file being there 3 months ago but it's not there today.  So, I go back 3 months, find the file and voila, restore it and all is good BUT, now a user creates a file one day, the daily incremental backs it up, the next day the file gets deleted and is no longer a part of a backup, the weekly does it's full and the monthly does as well and 3 months later the same question comes in for the file.  What I am looking for is, when a weekly is done, does it in fact take all previous incrementals and consolidates them into the weekly full OR is just taking a full snapshot of the server at that point and then the daily tapes just get overwritten thus forever deleting the file since it is not there at the end of the week?  I understand if a user creates a file and then deletes it before the incremental is performed the file is gone (not taking into account CDP constant data protection and shadow copies).  But, if I only have a monthly, would that file be there?  Does the GFS strategy take all daily files, consolidate them into a weekly then consolidates the weeklys into the monthy so everything would be there?  I hope this is not too confusing I just want to make sure that if a file is at least a part of ONE of the daily incremental backups that I can go back in 2 years and be able to restore the file.  Thanks!
Question by:ehouser_paralleltech
  • 2

Accepted Solution

CorinTack earned 500 total points
ID: 39621530
Short answer: No, a file created between the full backups would not show up on either full backup device.

Longer answer: When you create the full backup at the start of the week, it grabs all the files on the computer at that time. Each backup during the week then grabs the changes that have occurred since the last backup was taken, so that file would show up on the backup on the day that it was created. The next full backup, however, does not consolidate the previous weeks' (or months') backups, but instead just creates a new full backup of all files currently on the PC. So, in order to restore this file, you would need the backup from the one day that the file was created, prior to its deletion.

I hope that answers your question sufficiently.

Author Comment

ID: 39630555
Just to clarify, so what you are saying is logical since doing a traditional tape based backup would never "consolidate" backups to end up with one tape.  Maybe I am missing something here but to me, I would think you would want this type of backup so you can pick a file for example and the application would then show you the most recent (or all recovery points) for that item.  Taking an application such as Acronis for example.  If the backups are done in a fashion such as GFS and a retention period of 3 years.  They claim to run a process that will, based on a configurable time, "consolidate the files together and end up with one.  So, 5 daily backups and one weekly would be 6 and then the next week you would start over but the previous week was consolidated into one file.  This carries over again and again and the start of the next year, you see only one file for the entire past year.  You can then go through, find the file and restore that file as long as it was a part of at least one backup.  This obviously would never be practical for tapes but if you are doing disk based backups, it seems possible.

Expert Comment

ID: 39657877
Most traditional backup software does not work this way, no. Backups are not consolidated, but are taken as-is at the point in time at which they are created.

If you're looking at a software solution that states it does this, you should likely speak with the software vendor, or perhaps sending an e-mail to Acronis support to clarify exactly how this works and whether it will do what you want.

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