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I use Mac OS X 10.6.8. I have a brand new external portable hard disk, a Seagate 1 TB, formatted as NTFS. I want to use it as backup drive for Time Machine.

When I open Time Machine, it does not show my hard disk as an option that can be used for backup. Do I have to format my HD to some other type like FAT or EXTENDED? Do I need to download some software for making my HD work as backup disk?

Once it becomes my backup disk, can I use it for storing my other data from Windows or Mac too?

I read about using HFS+ formatted drives, but my Disk Utility does not show that option.

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In order to use your external drive for Time Machine, it has to be formatted with HFS+ (also called Mac OS Extended). OS X won't be able to write to NTFS partitions, and both NTFS and FAT don't support the features Time Machine needs to work properly.

Your only option is to format the drive. Go to Disk Utility, select the drive on the left, and then go to the Erase tab. Select Mac OS Extended (Journaled), which is the default, give it a name, and then click Erase…. Note that this will erase all data on the drive.

You can now use the disk for Time Machine. OS X should prompt you whether you want to set it up as a backup disk.

Windows, however, won't be able to write to this volume anymore. Linux may work, but the drivers for journaled HFS seem unstable, so it's not recommended to use this partition under other operating systems (so as not to screw up your Time Machine backup).

What you can do is partition the drive (see Partition tab) into, let's say two partitions, one being HFS+ for your Time Machine backup, the other being ExtFAT or FAT-32, both of which can be read and written to by OS X, Windows and Linux.

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When I tried this, I was unable to proceed. I kept getting the error:

 Disk Erase failed
 Disk Erase failed with the error:

 Couldn't unmount disk.

So I did a little research and found I had to turn Time Machine off first. (It had been on, but unable to back-up my Mac--hence the new hard drive.) So, little recommendation: turn off Time Machine before trying to format/erase/unmount the new drive.

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This is not an answer to the original question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – DavidPostill Dec 14 '14 at 21:54

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