Backups & restore points · Speed, progress and the first backup
Does Data Backup use space on my Mac's internal drive?
Short answer: Very little. The backup's working cache is kept on your external drive when it's connected; without the drive, backups still run using the internal disk temporarily. Versions live at your chosen destination.
Very little. The backup keeps a working cache so it doesn't re-read everything on every run, and Storage Studio keeps that cache on your external drive when it's connected, not on your internal disk.
If the drive isn't connected, backups still run — the cache temporarily uses the internal disk rather than letting a backup fail, and that temporary copy is cleared away later. Your backed-up versions themselves always live at the destination you chose.