Boot Camp failed and reduced Macintosh HD partition from 3TB to 1,46TB What went wrong? I created a new partition with Boot Camp Assistant (OS X 2,25TB | WIN 850GB), but during the partition process, the iMac suddenly restarted. When it got back on the Fusion Drive's (3,12TB) only partition (Macintosh HD) was only 1,46TB.

For the record; This is the first action I did after getting the iMac back from service where the hard drive was swopped with a brand new one. 

Short story:
Half of the drive is gone and I don't know how to restore the space that is gone.
I've tried First Aid in Disk Utility on both the Fusion Drive and the partition.

Below is all the disk info i could get. Hope anybody is able to help out.

OS X El Capitan, v10.11.1 (15B38b)
iMac (27", late 2012)


-- Updated diskutil list -- 

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *121.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Internal Drive          121.0 GB   disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3
/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *3.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage Internal Drive          3.0 TB     disk1s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3
/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +1.5 TB     disk2
                                 Logical Volume on disk0s2, disk1s2
                                 D0738033-EF3B-4A6E-B6C1-5E0D98477F4D
                                 Unencrypted Fusion Drive
/dev/disk4 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +3.0 TB     disk4
   1:                        EFI EFI                     209.7 MB   disk4s1
   2:                  Apple_HFS Time Machine-sikkerh... 3.0 TB     disk4s2


CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group F38D8AA1-92EE-421E-8DD8-EA44B88870C9
    =========================================================
    Name:         Internal Drive
    Status:       Online
    Size:         3120722075648 B (3.1 TB)
    Free Space:   1651571015680 B (1.7 TB)
    |
    +- Physical Volume D0B41875-348D-459C-B695-E67B7E86928F
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     120988852224 B (121.0 GB)
    |
    +- Physical Volume 2F916061-4E46-468A-B9AC-BB456BB2392C
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk1s2
    |   Status:   Online
    |   Size:     2999733223424 B (3.0 TB)
    |
    +-> Logical Volume Family E6B2F74B-9540-4043-92C7-446456885376
        ----------------------------------------------------------
        Encryption Type:         None
        |
        +-> Logical Volume D0738033-EF3B-4A6E-B6C1-5E0D98477F4D
            ---------------------------------------------------
            Disk:                  disk2
            Status:                Online
            Size (Total):          1463295803392 B (1.5 TB)
            Revertible:            No
            LV Name:               Macintosh HD
            Volume Name:           Macintosh HD
            Content Hint:          Apple_HFS
            LVG Type:              Fusion, Sparse
The first thing I would try is to open Boot Camp Assistant and see if you can remove the partition. Whether Windows was installed or not, this should be possible.

Alternatively, since I'm guessing you haven't repartitioned your drive since you installed El Capitan, you won't be able to resize the partition unless you use a source outside of your computer. Even in recovery mode, you won't be able to repartition. You might be able to resize it in Disk Utility if you use Internet Recovery: CMD + Option + R at boot. Another option would be to boot into recovery mode, install OS X on a USB drive, then from the installation on that USB drive, you would for sure be able to resize your partition.

I have done this many times, so I understand the frustration it can cause when you have space that you can't recover and the only way to get it back involves several hours of your time.

The good news is that if you ever start with a fresh partition in El Capitan, their new partition scheme is resizable even when you're using it live so you wouldn't need to ever even touch Recovery Mode.