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  1. #1
    Time Machine will not overwrite oldest backups.
    I am running Yosemite 10.10.5 on a 21.5" iMac. I am getting error messages saying "Time Machine couldn't complete the backup to ... This backup needs 495.76.37 GB but only 335.73 GB are available. Select a larger disk or make the backup smaller by excluding files."

    I was using a 500 GB external HD as Time Machine backup disk and started getting the same messages. I bought a larger 1 TB external HD only for the same messages to eventually appear.

    I understood that Time Machine overwrote the oldest backups as necessary so that the backup of current data is possible.

    Can anyone please advise me how to achieve this overwriting of oldest backups as standard Time Machine practice, please?

    Sincerely, PaulRanger1.
    Last edited by PaulRanger1; 03-17-2017 at 01:06 AM. Reason: Additional details.

  2. #2
    Time Machine will not overwrite oldest backups.
    Slydude's Avatar
    Member Since
    Nov 16, 2009
    North Louisiana, USA
    Your Mac's Specs
    2.8 GHz 2008 MacBook Pro 10.11, 8 GB mem, iPhone XS, 2015 iMac 16 GB 10.14.4 beta
    Rep Power
    Is the drive you are using partitioned in any way? If so check this thread.
    “Hard work beats talent when talent fails to work hard.”
    Kevin Durant

  3. #3
    Thank you Slydude for your kind response. I don't think it is partitioned as that is something I don't know how perform.

    After repeated software access problems, I reinstalled the OS X 10.10.5 from "OS X Utilities" window and all internal HD files were erased or overwritten. They had disappeared.

    With internal 'Disk Utility' open now, at top level (from among HDs listed on the left hand side of window), with "500.11 GB ST3500..." highlighted, Partition Map Scheme: shows "GUID Partition Table". This information is not shown when the item below that top item ("Untitled") is highlighted. "Untitled" is the name of my internal Macintosh HD but I don't know how to change it to that default title.

    I hope I have understood your question correctly (my fault).

    Gratefully, PaulRanger1.
    Last edited by PaulRanger1; 03-17-2017 at 02:13 AM. Reason: Clarity and dyslexic grammar

  4. #4
    Time Machine will not overwrite oldest backups.
    MightyGem's Avatar
    Member Since
    Nov 29, 2010
    Warrington, UK
    Your Mac's Specs
    PPC Mini, 10.4.11. Intel Mini, 10.6.8. MacBook Pro, 10.12.6. iPhone 5 iOS 11.3.
    Rep Power
    Have a look here perhaps:

  5. #5
    Hello MightyGem, Slydude et al,

    I think see from your 'pending' link the current cause of backup failures. The last "reliable" backup I had was dated 8 March 2017, before I erased the internal HD and reinstalled Yosemite 10.10.5 from the Disk Utilities window.

    Importantly, prior to the erasure and reinstall, the Time Machine had another 7 days backups in addition to the reliable b/u of the 8th March. However, System performance was compromised on 9 March or later and 8 March was the last reliable TM backup.

    Without any input from me, Time Machine deleted those other backups leaving me now with only one complete backup plus the (failing) backup 'in progress'. Hence the cause of the "Backup Failed" messages.

    Several points puzzle me, however. My internal HD used capacity is 445 GB while the newly purchased 1 TB Time Machine HD is 999.86 GB, more than enough to backup completely twice. I'm sure I must be missing something but what eludes me. I have ample spare capacity on a second 2 TB external HD with 1.23 TB available. If I copied the entire 8 March backup totalling 391 GB from the failing 1 TB Time Machine backup HD to the 2 TB external HD and erased the Time Machine HD, could that solve the current backup failures or will the same inane problem recur later.

    I am most grateful for your advice.

    Sincerely, PaulRanger1.

  6. #6
    Ah, new information! The fact that you erased the drive and reinstalled is a clue. When you did that, you probably created a new user on the new installation. If you did that, then TM sees that new system and user as totally different from the original system and user, even if you used exactly the same names. So, your used capacity is 445GB for the original backup (at least, probably more given the historical archive of that system) and the new used capacity is also 445 GB for the NEW backup, which is 890GB. Now along comes a big backup and you are out of room.

    At least that seems to be the sequence of events. And TM, as it does, deleted the old backup from that old machine to make room for the new backup. So far, it's working as designed.

    So, for the question. If you copied the entire backup from 8 March and then pointed to it as the backup file, I don't think TM will like that at all. Your newly installed system is a "different" system from the 8 March backup, even, as I said, if you used the same names. There are internal pointers and identifiers that are set at installation time and used by TM to enforce permissions and security, and those are now different between the 8 March backup and now. There MIGHT be a way to fiddle in the innards of OS X to get at those unique identifiers, but I would highly recommend you not try that approach. If it goes south, you lose everything and will have to do a full wipe and install again, putting you right where you are.

    Frankly, you might be best served at this point by doing that wipe and reinstall, though. And this time, when it prompts for you about migrating data at the first boot, before you create any accounts, say yes and point to the 8 March backup. That will reestablish all the proper identifiers and get you back to that date, from which TM should pick up the backup process. Even doing that, though, it may start with a full backup of the new state, so you'll be pushing that 1TB drive pretty full. Eventually TM should start to prune that older data.

  7. #7
    Hello MacInWin, Mighty Gem, Slydude et al,

    I am most grateful for your detailed explanation of how TM and its backup protocols work. Yes, when 10.10.5 was reinstalled, a new user (Untitled/Users/paulranger) was created. The home folder for the 8 March backup was Untitled/Users/paulcollins.

    Can you see any potential TM problems if
    I copy the backed up 8 March Users/paulcollins/Desktop folder only to my 2 TB external (in separate folder),
    open System Preferences/Time Machine and turn Time Machine off, close Pane (when copy is complete)
    erase the current failing TM backup drive in Disk Utility,
    reopen System Preferences/Time Machine and select (now erased) 1 TB external HD, close Pane?

    Will TM start/complete an initial backup of Untitled/Users/paulranger, overwriting old data as the remaining capacity requires, please?

    Thanking you again for your generous assistance, I remain

    Sincerely, PaulRanger1

    P.S. "Untitled" is my internal HD as I don't know how to safely rename it Macintosh HD.
    Last edited by PaulRanger1; 03-19-2017 at 08:50 PM. Reason: Grammar

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