Can I use a Seagate Expansion Drive with my Mac?

January 18, 2017 7:29 PM

I have a Mac Mini running OSX version 10.11.6. (El Capitan). With a view to eventually replacing its original 1TB internal disk with a smaller-capacity SSD, I bought a 4TB Seagate Expansion Drive.

Information found around the web suggests using Disk Utility to reformat this drive to OS X Extended Journaled and GUID Partition Map. Some of this information is a couple of years old so I'm not relying on it, but more to the point, when I try to erase, I immediately get a Disk Utility error saying the erase process has failed, and giving this additional information:

Unmounting disk
Couldn't unmount disk.
Operation failed...

I can move files onto the disk as it is, but it's a Windows FAT format now and I am antsy about this. What next?

posted by zadcat to Computers & Internet (4 answers total)

You _do_ want to format it as OS X Extended Journaled and GUID partition map.

Try the erase, let it fail, and try it again. Some program running behind the scenes is trying to use the external disk and won't give it up; typically, that's the indexing program that is part of Spotlight (the quick search dialog you get when you type command-space.)

You can keep retrying the formatting in Disk Utility and it will eventually succeed. You can also use the Unmount button at the top of the Disk Utility window, and then try to reformat the disk.

Nothing has changed about formatting a macOS hard disk in several years, especially the straightforward action you are attempting.
posted by blob at 8:40 PM on January 18, 2017 [3 favorites]

I'll add to what blob wrote: you can also tell Spotlight NOT to index your new disk, which may help:

1. Go to Apple menu > System Preferences > Spotlight

2. In Spotlight, click the Privacy button/tab/panel

3. In the Privacy panel, click the + at the bottom of the pane and add your new hard drive. After it's formatted, you can remove this block if you want Spotlight to index the new drive.
posted by mosk at 9:41 PM on January 18, 2017

Response by poster: Thank you both. It's done!
posted by zadcat at 9:50 PM on January 18, 2017

For the record, I had the same problem with the 1TB version of that drive. My solution was to use hdiutil, a command line tool. Man page. These brief instructions are good.
posted by Mo Nickels at 7:57 AM on January 19, 2017