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Backing Up Mac External Hard Drive Time Machine

About TM 'Backup Drive is Full' Alert

Time Machine Usb Drive

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  2. Time Machine is an excellent tool for backing up your Mac. But if your external Time Machine drive runs out of space or starts to fail, you might need to transfer those backups elsewhere. In this post, we’ve shown you how to do just that. Time Machine saves snapshots of your Mac from the past days, weeks, months or even years.

TM only deletes older files if they have been deleted from the source and when TM needs space on the backup drive for a new incremental backup. Time Machine 'thins' it's backups; hourly backups over 24 hours old, except the first of the day; those 'daily' backups over 30 days old, except the first of the week. The weeklies are kept as long as there's room.

Time machine is the best tool to Backup Mac to an external hard drive. If you are serious about your Mac backup, it is better to store the backup in cloud storage like iCloud or iDrive(75% Discounted link).

So, how long a backup file remains depends on how long it was on your Mac before being deleted, assuming you do at least one backup per day. If it was there for at least 24 hours, it will be kept for at least a month. If it was there for at least a week, it will be kept as long as there's room.

Note, that on a Time Capsule the sparsebundle grows in size as needed, but doesn't shrink. Thus, from the user's view of the TC it appears that no space has been freed, although there may be space in the sparsebundle.


Once TM has found it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start your backups anew or replace the drive with a larger drive.

Mac External Disk Drive

Time Machine sees the upgrade to Yosemite as a 'new' computer, so it wants to make a new, full backup separate from the other backup. Hence, there isn't sufficient space on the drive even after trimming old files. You have these options: a. erase the backup drive and start over; b. get another backup drive to use.

Backing Up Mac External Hard Drive Time Machine Ready

Nov 7, 2014 8:13 PM