does Time Machine delete or merge hourlies into daily backups?

Discussion in 'macOS' started by pna, Feb 6, 2008.

  1. pna macrumors 6502

    May 27, 2005

    I've searched all over the web, and in these forums, and still see a ton of confusion about how exactly Time Machine generates the daily backup from the hourly backups it created. I've seen postings on both sides of the issue, one arguing that it merges all of the files backed up in the hourlies into the daily (so all files present at any point in the day are present in the daily), or that it just selects one of the hourlies and uses that as the daily file.

    The former would make more sense to me, and be in more alignment with Apple's claims of "you're covered", but I can't find one definitive answer. Can anyone comment on their experience, or point me to a source that describes in detail how Time Machine creates the daily backup?

  2. Mark Morb macrumors regular

    Mark Morb

    Dec 19, 2007
    According to the Leopard "Missing Manual" the Daily backup is just the last Hourly Backup done on that day, the rest are deleted.
  3. netnothing macrumors 68040


    Mar 13, 2007
    I'm showing the opposite...the 1st hourly backup (done on that day, shortly after 12am) is saved as the daily.

    I'm showing that the weekly backup is based on whatever day you first started using TM. For example, I started using TM the day Leopard was released...a Friday. So for my weeklies, it is keeping every Friday backup and deleting the rest.

    As a general rule, this has been posted before and sums up how TM backs up files:


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