The backup disk is not in Mac OS Extended (Journaled) format, which is required.

captin lordsith,

you’ll need to run Disk Utility to format your new Toshiba drive to have the Mac OS Extended (Journaled) format.

Reformatting and erasing the disk:

From the Finder pull down on the Go menu to Utilities.

This will open the Applications > Utilities folder.

Plug in the backup drive.

> Disk Utility

> Click on the second left-justified icon (not "Macintosh HD").

> Parition

> Partition Layout > 1 Partition

> Options ... > GUID Partition Table > OK

> Format: Mac OS Extended (journaled)

> Name: Backup 1

> Apply

> File > Quit

 System Preferences > Time Machine

> ON

Unlock the lock if it is locked

> Add or Remove Backup Disk…

Choose Backup 1

In the upper right of the menu bar:

Pull down Time Machine to Back Up Now

From then on when your Time Machine disk is plugged in, Time Machine will make hourly backups.

I have a question. I too have the same issue an I currently have some data saved on my 2T seagate eternal drive. If I create a (mac journaled) partition using your above instructions will I lose the existing data or will it create a separate partition leaving the existing data on the drive?

Thanks,

You are awesome!! Perfect instructions! You got mine up and running quickly and easily! 🙂

at the last step i get a message of "

Partition failed with the error:

Couldn’t unmount disk."

Could you maybe help me with this please?

Sounds like you picked the wrong disk, what is the name of the disk you are trying to partition?

The name is 1TB Samsung M3 Portable - I am trying to create two partitions though - one for backups and one for general use? Currently there is an initial partition called Samsung, containing the system files of the external drive. I further get the same unmount problem with whatever I try to do with the disk. Also the current partition (Samsung) says that it is in the Mac OS Extended (Journaled) format yet Time Machine does not work due to the format problem.

In disk utility, what is the name of the disk you are trying to partition

Here is the screenshot

https://www.dropbox.com/s/7p5umfgvf9aa2f4/Screen%20Shot%202015-02-05%20at%2013.2 6.23.png?dl=0

And when I press apply, I get the unmounting problem.

Wow thanks so much hands4. That has sorted out my problem really easily!

I have a new Seagate slim backup plus for my MacBook Air . I havnt been able to use it bacuse "time machine" didnt have Mac OS Extended format.. I've followed the instructions re this issue.

I still cant back up with it. The message from the Time Machine application says Backup Disk Not Avaliable. .. it is pluged in, the light is on.. but its not working and there is no prompt. Can you advise.

Thank you so much!

I was just having this issue. Follow these instructions http://knowledge.seagate.com/articles/en_US/FAQ/007736en

Thank you so much for this information, its helpful.. Now my backup drive with time machine working.. Thanks a lot..