Does a Time Machine backup of a portable HD always have to start all over ?

Discussion in 'Mac Basics and Help' started by monarque98, Jan 8, 2015.

  1. monarque98 macrumors newbie

    Jan 8, 2015

    I have 2 external HDs, one static, one portable. The portable one I use for a portable photo/music Library to extend the limited space of my MacBook Air. The static one is plugged to my iMac and is a Time Machine backup for the iMac and the portable HD (I removed the portable HD from the "exclusion list" in Time Machine so it's included in the backup).

    Since the portable HD is not always plugged to the iMac, Time Machine sometimes backup only the iMac. When I plug in the portable HD once in a while, it includes it in the backup. However, and this is where my question is, it starts an entirely new backup (of like 700 GB) instead of backing up only the changes made since the last backup (that included the portable HD). Is there a way to avoid this ? If not, I guess Time Machine isn't yet a great tool for backing up portable HDs... ?

    Thanks you.
  2. Dark Dragoon macrumors 6502a

    Dark Dragoon

    Jul 28, 2006
    There is a bug with Yosemite and backing up external drives. I assume you are using Yosemite as other versions of OS X it should work fine.

    Instead of calculating the amount of data that needs to be backed up on an external drive, which wasn't connected during the last backup it just assumes that it all needs backing up.

    However once it has started the backup from what I remember it shouldn't actually need to backup the entire contents of the external drive again. Although as it assumes that the entire drive needs to be backed up this causes issues as if there isn't sufficient space to potentially backup the entire external drive even if nothing has changed, Time Machine will then remove previous backups in the mistaken attempt to free up enough space, and then if it cannot free up enough the backup will fail with an out of space warning.

    I've seen a few other people experiencing this, and I've got this issue myself. With prior versions of OS X it all worked correctly, so it's not that Time Machine isn't yet a great tool for backing up portable hard drives, it's that the latest version doesn't work correctly.
  3. monarque98 thread starter macrumors newbie

    Jan 8, 2015
    Thanks for the infos. I am indeed using Yosemite .

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