MacOS – Time Machine backup size seems to be too small

macostime-machine

It is my understanding that Time Machine does not compress as it backs up and that it backs up everything (at least in default mode).

Why then is the space-used stat given by Finder re my external hard drive to which I backed up my iMac's (OS X 10.9.5) internal drive much lower/less than the same stat in re my internal drive from which I backed up. The difference is 354.39 GB on internal vs. 85.83 GB on external.

My first backup took only about 40 minutes, which surprises me – thought would be like 4 hours, so I am wondering if it was complete and successful. However, all the files on my internal do seem to be on the external, and I got not messages indicating that there was a problem. It has been backing up hourly since that initial backup without any problems apparently.

Shouldn't those stats be the same?

Best Answer

Time-machine does not back up your entire Harddrive. It excludes most of the OS files and backups to your internal harddrive. It is possible, that you didn't notice, that your data got accidentially backed up to your internal drive. You can check it as follows.

To see how much space those local Time Machine backups are consuming, click the Apple icon on the menu bar, click About This Mac, and click the Storage heading. The “Backups” category here represents your local snapshots.

You can disable that through the terminal: sudo tmutil disablelocal

Edit: It will then automatically purge the already created local backups

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Mac – Time Machine – multiple backup destinations for a “separate weekly”

Basically, I would recommend not trying to constrain time machine to only a weekly interval on the offsite drive.

That being said, you can have both drives work totally independently as that is how the software is engineered. If you really only want a weekly snapshot, only connect the weekly drive once a week and force a rotation of the destination:

 tmutil startbackup --rotation

Once you have a backup to the weekly drive, eject it and send it away. As long as all dives get reattached every 14 days or so, you won't get a warning dialog that any are out of date.

Again, you can certainly enforce a single weekly backup by the procedure you follow but two things make that practice less needed than you might expect:

The backup intervals are very low space overhead compared to the size of cheap backup disks.

On my worst Mac, the system averages 5 MB of overhead for system log files so in absence of user files changing, you have 24 daily and 31 monthly snapshots you would avoid storing 275 MB (or 0.0003 of a one TB drive) if you were on a strict one per week schedule.

Since the cleanup of old backups is so fast and the storage impact so low, most clients with offsite rotation end up just swapping disks each week and let the software cull the extra snapshots per the normal schedule, leaving weekly snapshots more than a month old.

Time Machine Backup – Will it Store the Same Data Twice?

No, if you move the files back to another location on the disk backed up by Time Machine, the next backup will create a new copy of these files on your backup volume. This may even occur if you put them back into the same place (because the files will get a new creation timestamp which AFAIK triggers Time Machine to create a new file on the backup drive).

What you can do though is to navigate to the folder which originally contained the movies, open Time Machine from there, navigate back in time until the movies are displayed and then delete all backed up versions of them.

Best Answer

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Mac – Time Machine – multiple backup destinations for a “separate weekly”

Time Machine Backup – Will it Store the Same Data Twice?

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