I have a MacBook Air with 500G hard drive, only 270G being used. I have a 1T external drive that I use for Time Machine. After only a few backups, I can’t use it anymore. Time Machine says the remaining space is too small. Using Finder -> Get Info, I can see the external drive has 225G empty. What’s the minimum size to use for a Time Machine backup disk? I’ve seen recommendations of 5x and 10x, but what exactly is the minimum?
MacBook Air 13″, macOS 10.15
Time Machine doesn’t very do well with small output devices, particularly when there are larger files and file churn.
I’d look for 2.5 or 3 times the total capacity of the input volume. Or more.
The smaller the output volume goes and the closer to the capacity of the source volume, the less the depth kept, and the more effort needed for each new backup.
Time Machine doesn’t very do well with small output devices, particularly when there are larger files and file churn.
I’d look for 2.5 or 3 times the total capacity of the input volume. Or more.
The smaller the output volume goes and the closer to the capacity of the source volume, the less the depth kept, and the more effort needed for each new backup.
Not sure there is a specified minimum but it would be something along the lines of the total data being backed up, likely plus some kind of overhead to allow the backup to work. Your 1TB drive should be good for backing up for some time. It might be best to erase the drive and begin with a new Time Machine backup from scratch.
I have a 8TB external drive and 1 TB Mac drive (both are pretty full) that I back up to a 12TB external drive, and have for a while. There is still 3.2TB left as additional backups using Time Machine are incremental.
Minimum size for time machine backup?
