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  1. #1
    Have I done something wrong emptying Time Machine?
    pine man's Avatar
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    Have I done something wrong emptying Time Machine?
    Just recently I have been getting pop-ups warning that my Time Machine drive is nearly full. I checked and it is set to delete the oldest folders automatically so I did nothing.

    The pop-ups have started again so I opened up Time Machine and deleted the oldest folder by sending it to Trash and then emptying it. Everything seems to be ok but I didn't recover as much storage as I expected. The folder certainly appears to have gone.

    I now find that I shouldn't have done what I did but should have jumped through a few hoops with Terminal

    The Trash can is empty and the oldest Time machine folder has gone. Am I in the clear or will Time Machine eventually bite me in the bum?
    Peter - I used to be paranoid but now I just worry all the time.

  2. #2
    Have I done something wrong emptying Time Machine?
    MacInWin's Avatar
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    You have basically killed the TM backup. TM backups look like real files if you look at the drive with Finder, but the reality is that they are mostly just links to files that are elsewhere. Those links are chained together through the backups to provide the ability to resurrect previous versions when you do a restore. The entire thing is managed like a very complex database. By reaching in directly through Finder, you have broken the links, leaving files lost and the backup unreliable. Links are very small files, which is why when you deleted the links you didn't save a lot of storage. At this point about all you can do is reformat the TM drive and do a new full backup. All your history will be gone (actually, it's gone already).

    For the future, the only way to delete TM backups is through TM. You open TM go back in time and then use the Finder-like window to navigate back to the oldest backup, select the files you want to remove and delete them from the backup. All the links will be updated and the integrity of the backup will be maintained because TM will update the links.

    You can stop reading now, but I'll give a bit more on how TM works below:

    When you make the first backup, the real files are copied over to the backup drive as they are. When the next backup is done, the files that are NOT changed are not copied again, but links are created to the real file from the first backup. Links are very small pointers that look like files in the Finder window, but just point to where the real file is. Files that are changed are copied over as they are. On the next backup (the third one), again unchanged files are linked, but this time to link goes to the link in the second backup, which links to the original backup. That is done so that when you say you want a file from the second backup the links work. Changed files are copied over completely. In the fourth backup, files unchanged from backup three get links to the backup three file or links. Changed and new files get copied. Repeat this process over and over and you end up with some long chains of links for files that have not changed and some short chains for files that are more volatile and some new real files. At the end of a period of time, TM does an intelligent pruning of the links to summarize certain files in the backup. For example, after a week, hourly backups are compressed to one per day. Eventually backups are compressed more by editing the links to have one per week. The logic is that you are more likely to need a file changed in the last day or so than to have to reach back into months ago, and if you DO go back months, the file is unlikely to have a lot of volatility, so a relatively good copy from one week should do. TM then updates all the links so that as you go back in time, you can find the real data for that particular instance of the backup.

    For a more graphic presentation of how TM works, see this: Welcome to iCanHelpYourMac.com! Tip Archive : Understanding Apple's Time Machine. What is Time Machine? How does Time Machine work? | Reliable Macintosh Service and Support servicing the Brainerd Lakes Area. How can I help you?

    Bottom Line: You cannot make changes in TM backups through Finder as Finder does NOT update the link chains. Only TM does that.
    Jake

  3. #3
    Have I done something wrong emptying Time Machine?
    pine man's Avatar
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    So my bum has been well and truly bitten!

    I could kick myself - who carries out an operation and then afterwards Googles it to see how it should have been done!!

    Thanks for your excellent explanation, I'll do as you say and reformat and start all over again. I also run CCC alongside Time Machine so hopefully I'll be ok.

    Hey Ho.
    Peter - I used to be paranoid but now I just worry all the time.

  4. #4
    Have I done something wrong emptying Time Machine?
    MacInWin's Avatar
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    The CCC backup is a very good thing to have, particularly if you have the Safety Net function turned on. While not as intuitive as TM to get back in time, changed files are kept in the Safety Net folder by date, so you can at least go back a bit. The difference is that CCC does not use links, so the drive fills up faster and CCC has to prune the Safety Net more often.

    In future, just let TM clean up the drive as it needs to. About the only time I've seen TM choke was when the TM drive got very full, I had turned off TM for a while and then turned it back on and a file that had changed was larger than normal (a Photos database, as I recall). TM then could not decide what to do and sent me an error message. I think if I had not turned TM off it would have been able to clean up the drive, but it got overcome by too many changes at once.
    Jake

  5. #5
    Have I done something wrong emptying Time Machine?
    pine man's Avatar
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    Thanks for that.

    TM threw the first pop-up when it was quite full and I downloaded an update for my satnav, which was 16GB and far bigger than the space on the EHD. It never seemed to recover from that shock and, even though I eventually deleted the satnav update, it still kept throwing pop-ups. It was then that I carried out the dastardly deed. As I type TM is backing up my HD.

    Thanks again.
    Peter - I used to be paranoid but now I just worry all the time.

  6. #6
    Have I done something wrong emptying Time Machine?
    MacInWin's Avatar
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    Yep, that will trigger it. I do like TM, but it has quirks in how it manages a nearly-full drive. Right now I'm backing up to a 4TB drive that has more than 2TB free space. I use TimeMachineEditor to schedule backups for just twice a day, noon and midnight, as I don't have a business need for hourly backups. So the space for TM is growing slowly. I do use the drive for other storage, but that is a "deep" storage of files I want but don't use frequently. The drive was relatively cheap because although it's large, it's slow, but for a TM backup, I don't care.
    Jake

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