Double "Fusion" drive on startup

Hello purpleduck,

It looks like your drive is duplicated in the boot screen for some reason. I would recommend verifying the disk with the Disk Utility. The following article will help you do that:

Disk Utility 12.x: Repair a disk

http://support.apple.com/kb/PH5836

1. Print this help page so you can refer to it later. (You don’t have access to Disk Utility Help when you restart up your computer in the next step.)In the Disk Utility Help window, choose Print from the Action pop-up menu (looks like a gear).
2. Choose Apple menu > Restart. Hold down the Command (⌘) and R keys as your computer restarts.When you see a white screen with an Apple logo in the middle, you can release the keys.
3. Click Disk Utility, and then click Continue.
4. In the list at the left, select the item you want to repair. (Be sure to select an item that’s indented to the right in the list, not an item at the far left.)
5. Click First Aid.
6. If Disk Utility tells you the disk is about to fail, back it up and replace it. You can’t repair it.
7. Click Repair Disk.If Disk Utility reports that the disk appears to be OK or has been repaired, you’re done. Otherwise, you may need to do one of the following steps.
8. If Disk Utility reports “overlapped extent allocation” errors, two or more files occupy the same space on your disk, and at least one of them is likely to be corrupted. Check each file in the list of affected files. If you can replace a file or recreate it, delete it. If it contains information you need, open it and examine its data to make sure it hasn’t been corrupted. (Most of the files in the list have aliases in a DamagedFiles folder at the top level of your disk.)
9. If Disk Utility can’t repair your disk or it reports “The underlying task reported failure,” try to repair the disk or partition again. If that doesn’t work, back up as much of your data as possible, reformat the disk, reinstall Mac OS X, and then restore your backed-up data.If you continue to have problems with your disk, it may be physically damaged and need to be replaced.

Thank you for using Apple Support Communities.

All the best,

Sterling

@ Purpleduck: exact same thing here!? Have you somehow managed to solve it?

By the way: I ran Repair Disk and it showed no problems at all.

However, in SystemPreferences when I choose StartUp disk I only get one FusionDrive available?

SSD is Samsung Evo840 120 GB + stock WD 500 GB Hard Drive.

Confused...

Same exact thing here. I noticed my two fusion drives appearing in Disk Utility. The only reason this happened is because every time I tried to install bootcamp it failed and I have successfully installed bootcamp on every other machine I have owned. This is an iMac 32Gb 5K 27 Late 2014 ... really Apple? Windows booted on flash drive and mouse and keyboard would not work ... tried with a disc after the bootcamp flash failed also no mouse and keyboard ... pretty pathetic. Now, my fan roars non-stop and I have two fusions each listed as 3.11. This is kludge ... seriously upset, and losing errors after trying to use common built in functionality the proper way and the way I have done before. I am already trying restore and just checking resources on my laptop and pretty furious this is a common error and Apple has not fixed it yet since this is late 2015 and I only bought this iMac this summer just before the mis 2015 came out ... pathetic!

Recover mode and the Disk Utility within it did nothing except fail to unmount. After some investigating, here is the only solution that worked listed below. However, thankfully I had made a full back up before I started tinkering because this fix required completely deleting everything and refusing. Instructions:

1) Command R Boot

2) Run Terminal

3) enter:

diskutil unmountDisk force /Volumes/[put "Volume" name here no braces]

This unmounts the "volume"

4)enter diskutil list

Find the identifier for the disk that is giving you trouble.  It will be something LIKE but not exactly like disk1, disk2, etc.

5)diskutil eraseDisk JHFS+ Everest /dev/[put "Identifier" name here no braces]

Wait until terminal completes operation.  You will see some percents and some progress.

6)Quit Terminal

7)Open DiskUtility GUI (or if you know how stay at command line and refuse there but this is not advised.)

8)Select Macintosh HD (now red with no Volume underneath).  Partition it.

9)DiskUtility will automatically prompt you to refuse and fix the drive.  Do so.

Done. There is a related post to this on the forums, but the person was able to do this all with the GUI. For those with two fusion drives appearing (ridiculous as that seems), this is required as far as I can tell because the GUI has some type of fail safe to avoid allowing unmounting.

Picture of the two volumes from Disk Utility to add to the gallery of doubled volumes ...

Thanks Apple ... in my attempt to install Windows 10 on my machine, I ended up losing nearly 30 hours of time researching, waiting, reinstalling, and re-authorizing tons of product keys due to too sensitive a bootcamp process ... it reminds me of when bootcamp first came out ...

On Macs with 3TB fusion drives, the Bootcamp partition is sandwiched between two separate parts of a single CoreStorage volume. This is to account for legacy Windows installations which require a MBR/BIOS which has severe limitations. This can show up as two separate CS volumes, which many tools report as two separate Fusion drives. Your screen shot indicates that ELC still has not fixed the bug reported in earlier OS X versions. 😟