Partition issue, couldn't unmount disk (error)

You may not have a firewire port, but you probably have thunderbolt. Buy a thunderbolt > FW800 adapter and boom, you now have a firewire port. I just used one of these along with a FW800 > FW400 adapter and a FW400 cable to bring an older mac up to Lion.

Apple took way too long in releasing this adapter, but it's been out for awhile now and it's an invaluable tool. Target disk mode still exists for this reason, but I don't think most folks know about that adapter or the idea behind it's use.

Open Disk Utility> First Aid tab, and click the Repair disk button on the bottom right corner.

This worked for me. It repairs permissions and in trying to solve this problem for my disk I eventually discovered in Terminal that the external hard drive was saying I "didn't have permission" to write.

So, Give Repair Disk a go and good luck.

Spent many hours trying to figure this problem out. Did every step I could find, from going into terminal and trying manually formatting the disk, to using Disk Utility.

Here's what acutally works. No. Seriously. THIS WILL WORK.

1) Buy a 16 GB flash drive.
2) install Disk Maker X on another Mac.
3) Download your version of OSX.
4) Using Disk Maker X and your new 16GB drive, create a bootable install drive.
5) Boot to that recovery drive holding the option key at startup.
6) Select Install OSX, and choose the same USB drive that you are booted into at the moment. Let computer restart and install OSX.
7) Once you're into the booted OSX drive after install (this is slow, so be patient... you're running the entire computer off a slow USB stick) right click on the drive that isn't unmountable in Finder. CLICK EJECT. It will probably tell you that there are applications being run on the drive. Push through and force EJECT.

8) Open Disk Utility and click the HD that you're trying to format. Click Erase and format the drive.

9) Go back into the Finder and open the OSX Install disk that is on the USB drive.
10) During installation select SHOW ALL DRIVES and select the drive that you just formatted.
11) DONE. FINALLY!

<Edited By Host>

Hey guys! I figured it out.

1. Create a Time Machine backup on a separate hard drive.

2. Restart computer and hold the option key

3. It will show all the hard drives you can boot into. Click on your external hard drive

4. Go into your disk utility like normal and then take out the partitions. It won't give you any crap now,

HEY MAN!

I FOUND THAT I GET THIS ERROR WHEN BOOTING BY HOLDING DOWN "U" AND BOOTING FROM AND EXTERNAL SOURCE.

BUT...

IF I BOOT USING THE "U" METHOD ... THEN... CHOOSE "STARTUP DISK" AND SELECT THE USB SOURCE... I AM THEN ABLE TO FORMAT THE DRIVE.

TRY SELECTING "STARTUP DISK" AND REBOOT FROM WHATEVER EXTERNAL SOURCE YOU ARE USING.

THANKS!

What's going on here is that most of us are actually talking about different problems and solutions that will only work on some computers. It is my opinion that goldfish had the same issue as me, in that there were partitions previously to upgrading to Lion, which caused a problem during the hot partitioning of the disk when the Recovery HD was added. This problem may have been causing, or might have been separate from and only have been compounding the issue wherein we were unable to successfully get to the external Recovery HD. Our computers were refusing to boot to the external disk, and this was difficult to recognize because they are identical and it is counter-intuitive to assume that the selected boot volume was being ignored in favor of the internal disk everytime.

A lot of the offered solutions that follow fail to recognize that goldfish could not unmount the internal volumes because he was not booted to the external drive afterall. The only way around that problem was to delete the internal Recovery HD and thus preclude any possibility of booting to it.

Also, I think, but am not sure, that the suggestions to change the partition map on the live boot volume will not work if there is a hidden Recovery HD.

And no, d34dfish, that computer i had did not have a thunderbolt port, only a minidisplay port. That particular revision of the macbook air was lame.

That *****- the gap between FW and TB is a big one. I was afraid to buy anyting while it was happening and still suffered a bit since it took them forever to get the TB > FW adapter out.

Can you boot to USB image of the OS? I just created one for a client when mavericks woudln't load on it's own and it worked great. I wish I had a machine with this issue so I could play with it a bit and try to resolve it myself.

Sorry my tip didn't help!

Ok, I see a lot of the same responses to this problem. ..none of them work for me.

I have an early 2008 Macbook Pro, Intel based with OS 10.9.2 Mavericks installed.

I had some issues that prevented me from booting into safe mode, so I got in through Daemons to get my data backed up. HOWEVER, I had to back up files online because since the file corruption external drives do not show up...not in DU (launched or in Recovery mode) or in terminal.

So, I'm in Recovery mode. I have erased and chosen extended journaled for the format. My drives are just a main partition and a 37 gb time machine partition.

Under that on the left "disk 1" Main OSX.

When I try to adjust the partition, I also get the error of "Can't Unmount drive".

When I click 'repair disk' on the main partition, BDGibbs, it says that the volume is ok. When I try this for the hd, it says that it's not supported live.

I can't seem to erase, mount, adjust partitions or anything with this drive.

When I try to reinstall OSX...The only drive I can install it on is BDGibbs. It shows that the Recovery drive is locked...

But when I select "Startup Disk" from the Apple icon, it doesn't show any bootable drives.

When the OS is reinstalled, instead of restarting, it goes back to the Recovery mode main menu. When I manually restart...it boots back to Recovery mode without holding any keys. I've even hard booted and still automatically back to RM.

Please help. Again, my laptop is not recognizing external drives so that is not an option. Is there something I am missing here?

@BD_Gibbs...

I MADE A MAVERICKS USB INSTALL "THUMB DRIVE" AND BOOTED FROM IT. THEN I CHOOSE THE "THUMB DRIVE" AS THE BOOT DEVICE IN THE INSTALL SETUP. I REBOOTED...

I WAS THEN ABLE TO ERASE THE OLD OS DISC.

1: BOOT FROM USB INSTALL OR OS DVD INSTALL

2: CHOOSE THE SAME DEVICE YOU JUST BOOTED FROM AS THE STARTUP DISC.

3: REBOOT.

4: NOW YOU CAN UNMOUNT / ERASE THE OLD OS DISC.

BASICALLY... YOU ARE FORCED TO BOOT FROM AN EXTERNAL USB OR DVD IN ORDER TO CORRECT THIS.

"RECOVERY" MODE WILL NOT WORK.

TRUST ME...

JEFF

Message was edited by: SKULLYARD

Ok, I can not get a USB drive to register....

But after actually speaking with Apple... you can start from Internet Recovery Mode. Command + Option + R. It will be the same as booting from a recovery drive on an external.

I have had the same issue for a long time now. Partitioned Bootcamp so I could do some school work that required windows OS. I was able to delete the Bootcamp partition but to restore the full size of my main partition, nothing worked, always got the error where it could not unmount the drive. Booting into the internet recovery by starting up while holding cmd opt r, going into disk utility and then dragging down my main partition back to max worked, FINALLY, with no issues at all.

Thank you, thank you and thank you again! Here is a man that know what's he talking about! I did not however use DiskMaker X, I used the "DU" and followed your directions and it worked!!! Thanks a bunch!

Goofiest solution worked for me. Background: I erased Bootcamp from my macbook pro, and then had issues repartitioning my hard drive. I was unable to get rid of the partition that the Bootcamp program occupied. I got the "Partition Failed: Couldn't Unmount Disk" message. I searched a lot of other possible solutions, but then I finally stumbled upon Geoffist's solution and it worked on my first attempt.

If none of the disk utility and external boot options are working for you try this. It worked for me after hours of forums and confusing posts. Simple and effective and now I was able to erase my disk and it mounts.

http://technology.siprep.org/fix-for-disk-erase-failed-couldnt-unmount-disk/

I found my answer for unmounting my disk by eplt@odwon this similar thread.

https://discussions.apple.com/thread/4117187