DU "can't unmount disk"?

[clyde]

Want to use an external drive for Time Machine, so thought I'd erase the ext drive first. It is partitioned, so I told Disk Utility to erase the larger partition. It started, quit, and said: Can't unmount disk.

What does this mean? It will erase the other partition…

[clyde]

Clicked "follow topic"

[PeterW]

Restart the computer. Then try the erase again.

[jdc]

PeterW wrote:
Restart the computer. Then try the erase again.

This. Fixes 99.999% of everything.

[GGD]

Quite often the reason why you can't unmount a drive is because as soon as it's mounted, Spotlight grabs it and starts indexing and won't let go.

Sometimes repeated unmount attempts will eventually work if you catch it just right, sometime putting the computer to sleep and then waking it and quickly clicking the unmount button before Spotlight resumes will work.

In the old days, booting from the install DVD and running Disk Utility from there was the best way to manipulate drives because Spotlight wouldn't run at all.

[Onamuji]

If you're erasing it then you don't have to treat the contents with special care. Stuff that might corrupt the directory structure is fair game because you'll be making a nice clean new directory-structure.

Eject from the Finder and when it tells you that the drive is busy and asks if you want to force-eject it then opt to do so.

Then you'll be able to erase it with the DU.

[Robert M]

Clyde,

An app might be accessing the drive. Spotlight is the likely culprit. You can tell it to not index the drive in the spotlight settings and see if that makes a difference. You may also want to grab a copy of Mountain. Great little app. It'll tell you which app is using a volume and stopping it from unmounting.

Robert

[PeterW]

So, what did you try and did it work?