Time Machine & Backup Size

krawfo

macrumors regular
Original poster
May 4, 2011
150
7
I'm backing up a 1TB drive that has 532GB of data on it. I formatted a 1TB drive and configured Time Machine to exclude Apps, Caches, System Files, etc. Estimated full backup size is 331GB. Twenty one days later my backup drive is full.
Obviously, I'm missing something. I can't figure out why 532GB of data has filled a 1TB drive.
Any insight would be appreciated.
 

krawfo

macrumors regular
Original poster
May 4, 2011
150
7
Thanks for the reply. Pardon my ignorance, but what do you mean by "loading the drive".
 

Weaselboy

Moderator
Staff member
Jan 23, 2005
29,403
8,989
California
I'm backing up a 1TB drive that has 532GB of data on it. I formatted a 1TB drive and configured Time Machine to exclude Apps, Caches, System Files, etc. Estimated full backup size is 331GB. Twenty one days later my backup drive is full.
Obviously, I'm missing something. I can't figure out why 532GB of data has filled a 1TB drive.
Any insight would be appreciated.
Time Machine (TM) keeps versions of files, so for example, if you have a 2GB video that is backed up to TM and you edit that video... the whole 2GB video gets backed up again taking another 2GB of space on the TM disk.

Another example.... you download a 3GB video and watch the video, then delete it. If TM happened to do its hourly run during the time that video was on your system, that is another 3GB on the TM disk.

The same thing happens with any documents or anything else you edit. All these versions get saved to TM. Over time that can add up.

Just a suggestion. You don't need to exclude caches etc fem TM backup as those are excluded by default. I would just let TM backup everything so it could be used as intended for a full restore id disaster strikes.
 

snberk103

macrumors 603
Oct 22, 2007
5,539
87
An Island in the Salish Sea
TM is working as designed. This is because TM is not a simple backup, but a versioning back up solution. It is designed to allow you to go back and retrieve documents that you may have deleted, or to retrieve earlier versions of a documents that you may have overwritten. Since these different versions need to be stored, a TM disk will fill up. When a disk becomes full, TM will delete the oldest versions to make room for the new. The bigger the TM disk, the older the documents that TM will be able to save for you. What Weaselboy wrote is correct...

In my case I use a cloned backup (runs automatically at night) to make a bootable backup of my system. I'd use this to recover from catastrophic hardware failure. I also use TM - which I use to recover from user errors. That is... to recover files I've deleted or overwritten when I shouldn't have. My cloned backup is also cycled to a safe off-site location.

Hope this helps.
 

Tumbleweed666

macrumors 68000
Mar 20, 2009
1,651
47
Near London, UK.
I'm backing up a 1TB drive that has 532GB of data on it. I formatted a 1TB drive and configured Time Machine to exclude Apps, Caches, System Files, etc. Estimated full backup size is 331GB. Twenty one days later my backup drive is full.
Obviously, I'm missing something. I can't figure out why 532GB of data has filled a 1TB drive.
Any insight would be appreciated.
Chances are you'll be frequently altering one or a small number of very large files.