Time machine question

Discussion in 'Mac Apps and Mac App Store' started by MrMister111, Feb 5, 2019.

  1. MrMister111 macrumors 68020

    Jan 28, 2009
    Is there a way to "force" time machine to backup on my usb connected drive?

    The problem I have is my usb drive is 1.5Tb and my iMac is a fusion of 1Tb and although first backup went ok, it now won't backup as not enough space says on time machine drive.

    I know the premise is to make numerous backups of history so needs more space, but it's there a way to just force this backup so I at least have a current backup?

    I will buy a bigger usb drive (any suggestions?) eventually but just for now?

    I used to have a time capsule but didn't need the router side anymore so was wasted a bit so sold it.

    I do have a Seagate personal cloud NAS drive which I think supports time machine, but not sure if it's in the correct format or if you have to reformat it etc, it currently has 2Tb free so not sure how much TM would stay to use up either as also want it for my other files, it's a 4Tb in total HDD NAS

  2. niji, Feb 5, 2019
    Last edited: Feb 5, 2019

    niji Contributor


    Feb 9, 2003

    interesting problem.

    i was always under the impression that Time Machine just deleted old backups, but have never understood very well at what point that deletion would start to occur.
    i found this support discussion useful for my own understanding.

    it starts out:
    "The oldest backups will be deleted when Time Machine requires the space they occupy, but they will only be deleted after Time Machine creates a new backup. Apple does not provide guidance for the backup device capacity because it is simply not possible to do that. Two or three times the total amount of data that needs to be backed up is usually OK."

    i have also found that a Time Machine drive with triple (3x) the size of the data amount i am backing up never has resulted in any noticeable overwriting of any my data on my Time Machine. but it would depend on how much new material you are adding daily, and as well as how much you are deleting as well. so i can understand the difficulty there is to describe it more precisely other than stating at what intervals there are weekly and monthly snapshots and at what point those are going to be deleted.
    but i have also never kept old Time Machines much longer than a year anyway, since I alway like to start with a fresh backup to Time Machine every time there is a major new macOS release.

    link to full discussion: https://discussions.apple.com/thread/8213715

    the best backup medium for me that i have started to use about 6 months ago is the SanDisk Extreme SSD. works perfectly with Time Machine. unbelievably fast. really happy with it.
    i bought 2: one for time machine and one for ad hoc backups of irreplaceable info (photos, business files, 10 years (!) of email, etc,

  3. cruisin macrumors 6502a


    Apr 1, 2014
    When you are moving files, the actual hidden process is a copy followed by a deletion. For backups this also happens, as a backup can fail for many reasons and pre-deleting files defeats the point of a backup. It will make a backup then it will do a cleanup to generate more space. So you would need to delete the existing backup and make a new backup to force the backup to happen.

    2x the drive is a good minimum, but you will lose out on long term history, likely will be limited to 1 month or less. If you are using the full capacity of the 1 TB and doing things like making large amounts of changes then the history might be measured in days. Since you are having problems with 1.5x then 2x might also cause problems as Time Machine copies whole changed files and not just the changes (doesn't do deltas of changes). If you do a tiny edit on a 4 GB video then the next backup will copy the whole video again.

    If you want to prevent Time Machine from eating all the free space (because it will use all the space as it is just a special folder that it fills with your stuff) you could divide the external into two partitions, so that it will only backup to the part you specify (but for less headaches you should consider a dedicated drive).

    The partitioning might erase your existing drive. Also make sure that your external drive has its own backup, as it can break just like your Fusion Drive. And consider that local backups only protect against the drive dying or accidental deletions. If you have anything that would be lost after a fire or theft you should consider a 3rd backup either in the cloud or something like a safety deposit box.
  4. MrMister111 thread starter macrumors 68020

    Jan 28, 2009
    Thanks for answers and explanations. I think to use my NAS is going to be too much of a need on, and then also it will be reading/writing all the time also which could reduce life of it.

    I may just buy a USB drive and use exclusively for TM then. Is a USB powered a suitable option rather than having a one powered from wall socket?

    As my fusion drive is a 1Tb, and as discussed above, and maybe to try and future proof a bit may get a 4Tb one.

    I also have an online backup service I subscribe to so am protected off site also.

    Seagate 4 TB Expansion USB 3.0

  5. glennsan macrumors regular

    Jul 16, 2002
    San Diego
    I have only USB (bus) powered drives. I love the ability to take them without having to reach down and unplug from the wall.
  6. Howard2k macrumors 68000


    Mar 10, 2016

    Your NAS almost certainly has drives that are made for NAS and suitable for greater read write cycles. I would not be at all concerned about that.

    The two things to be more concerned about are:
    * Gigabit Ethernet connection for initial backup
    * Don’t rely solely on NAS TM. I recommend continuing to use one or more external HDDs as TM targets. Advtange is you can also move them around.

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