Time Machine Disk Backup Size

Discussion in 'macOS' started by kevn, Mar 24, 2011.

  1. kevn macrumors newbie


    Jan 21, 2011
    I just ordered a 1 Tbyte external hard drive that I want to use for Time Machine backup. My internal iMac hard drive is 1 Tbyte. I only have about 100 Gbytes on the iMac right now, but I am a little worried about not having ordered a larger backup drive, because since I ordered it, I've read recommendations of 2X or 3X for the backup drive. I have not seen a minimum requirement for this on the Apple website.

    Will I eventually run into problems because the external drive is not larger than my internal drive? If my internal drive volume approaches being full, will I still be able to restore from Time Machine backup disk of the same size, to at least one or two backup dates?

    I understand that, as my hard drive fills up, there will be fewer and fewer backup dates available on the Time Machine backup disk, but I don't have a sense as to how much of a problem this is if the boot disk size = the Time Machine backup disk.

    thanks! Kevin
  2. MacForScience macrumors 6502


    Sep 7, 2010
    Won't be an issue until you have a lot more data on your drive. The reason most recommend 2x or 3x the size is because of how many weeks of backups you can store. If your drives match in size, if you fill your internal (bad idea) you will have an issue with not enough backup space for more then one full backup. You have to remember that TM doesn't perform a full backup each time it performs small incremental backups. This means that when your drive is full TM can only store what you have as a single copy with no previous versions.


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