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If I delete photos from my current iPhoto library which have been backed up on time machine, will it be possible to recover these photos from my time machine backup once they've been deleted from my hard disk/iPhoto library? or will time machine eventually delete them next time I backup? does time machine keep my backups for a particular period of time before deleting them to make room for the next round of backups?

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3 Answers

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By default, Time Machine keeps the following backups:

  • Hourly for the current day
  • Daily for the past month
  • Weekly for all the other months

If there's space constraints then Time Machine will start to delete the backups, but otherwise it keeps them for as long as possible.

To get to the individual photos you will have to have iPhoto as the active window when you activate Time Machine from the menu bar. This lets you go back and see all of the photos. If you did it from the Finder it's more complex because iPhoto bundles its whole library into one big package.

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Do be aware that I had a friend add an external hard drive to their mac. It was 1TB and Time machine was told to back it up. My friend ended up with Time Machine deleting everything except for the backup from the day before so only having one copy on the Time Machine means a software bug or change in the system can make them get automatically deleted with no warning or chance for you to save them. –  bmike Jun 21 '11 at 15:44
    
Do you mean that time machine was told to back up to this harddrive or he told it to back up the actual harddrive onto another. There is a setting in time machine preferences to warn when it is deleting old backups, so that can be helpful in this case as well –  shadesandcolour Jun 21 '11 at 19:22
    
I believe external drives default to be excluded from Time Machine. My friend absolutely clicked the button to include those drive over a period of months. Just that they were not all present and loaded with data until later when the surprise delete event happened. It was user error to be totally clear. It's just understandable how it happened in hindsight. It was too easy to delete all the backups - I feel Time Machine should delete one or two backups and then warn/stop - not erase 15 months of backups due to a sudden increase of disks attached. –  bmike Jun 21 '11 at 20:02
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Time machine automatically deletes files off the backup drive in two cases:

  1. Hourly backups expire after 24 hours and daily backups expire after 31 days
  2. When the drive doesn't have enough space to start a backup, old backups are permanently deleted.

The hourly backups fold in to one daily backup - so if a file A was backed up at 2 pm and file B was backed up at 4 pm, even though those backups get deleted, the files all fold into the remaining hourly backup that then becomes that day's backup. Similarly after a month - up to seven daily backups get folded into a weekly backup. You should be able to go back to get any photo you deleted during this period of folding and deleting by going to the closest time to when the file was added or changed.

The real problem is that the system is allowed to delete any backup except the most recent once the backup disk is full. So if you deleted some Fall pictures several months back - if the system feels it needs more space for a backup, it will delete all your old photos. Even if you select the warning, the system warns you after the deletion is complete* that they are already gone. Most of the time, you don't lose the entire history, but I have seen that happen twice

Two friends were really surprised to find one day their time machine only had one hours worth of backup.

One time it was a bug or an error - the system thought it needed 100TB of space and it deleted all the old backups except the one from one hour in the past.

Another was a friend that kept adding external drives over time for photo storage and adding them to Time Machine. The iMac only had 200G used on the 1TB drive, but three external drives with 300G of photos each caused the same deletion of all the old backups. The 1 TB time capsule couldn't hold all the files and deleted all the old backups and then popped up a message that it couldn't even start the backup process.

I don't mean to make it seem like Time Machine is bad - just that I am in the practice of having a second hard drive to make yearly backups of all photos before I do the deleting. Time Machine is great to save me from myself accidentally deleting something as well as protect from a failure of my mac but I don't trust it to be the only storage place for something I may want later.

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Time Machine will keep old versions deleted/modified files for as long as it has disk space to do so. There's no fixed period of time, but given that Time Machine only stores files that have changed, the odds are pretty good it will keep it for a long while. It ultimately depends on the size of the your back up drive, the size of the disk you are backing up, and the cumulative size of files you change in the future.

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