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When I manage my Windows 7 Backup's disk usage through the "Manage space used by this backup" and then "View backups..." options, I see two backup periods.

Windows 7 Backup Disk Periods

That report implies I will free up 1.14 TB if I delete the "12/9/12 to 1/1/13" backup period and leave 84.49 GB of backup data untouched. But how is that possible? My backup target(s) total 517 GB, far more than the second period.

So I am wondering...

  1. Will Windows Backup preserve/promote the file data required for "1/2/2013 to 1/5/2013" to remain a complete backup, therefore resulting in a "1/2/2013 to 1/5/2013" backup period that is 500+ GB in size?
  2. Or will Windows Backup discard everything discovered during the "12/9/2012 to 1/1/2013" backup period, even if the newer backup period needs it, therefore leaving the backup largely incomplete until another backup is performed?

The dialog says "All files backed up during the selected period will be deleted," but I find it surprising that I should have to forfeit ~80% of my backup (a huge date range of incremental data), and then run it again before a disk failure, just to free up some space on the backup target.

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1 Answer 1

The granularity for deletion is a backup period, which represents a full backup together with its associated incremental backups.

source

Each backup period should be self-contained, and unaffected by the (non-)existence of other backups. There are several possible reasons for the size difference:

  • The smaller backup period is only over 3 days, compared to 23 for the larger backup. With a period almost 8 times longer, a larger size is expected.

  • Since this is an incremental backup, an initial full backup is taken and then any changes will be backed up on top of that. If you have made a large number of changes on the drive and/or have a very short time between backups, a larger size is expected. If you change 50 GB of data every day (with a daily backup), that would be 2.65 TB worth of changes that will be backed up over 23 days.

  • A combination of the above


Also, there is a known bug that may result in some files being backed up each cycle, despite being 'unchanged' (if a media service updates the metadata): http://support.microsoft.com/kb/981470

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