Missing partition in my iMac Fusion Drive - can't do school work! I did a dumb thing while messing around with Boot Camp and managed to lose a partition that I had made earlier to install Windows on to.

A 300GB partition is now missing and I've tried everything since this morning to get it back but I clearly lack the knowledge and I need my Mac for school work.

Do you have any suggestions on how I can restore the lost partition without a backup?

Thank you!

    diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            699.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

/dev/disk1 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         24.0 GB    disk1
   1:                        EFI EFI                     314.6 MB   disk1s1
   2:          Apple_CoreStorage Macintosh HD            23.6 GB    disk1s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk1s3

/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            Macintosh HD           +722.0 GB   disk2
                                 Logical Volume on disk1s2, disk0s2
                                 9449131B-67F8-4D97-82D6-F2BDEDB48B6C
                                 Unencrypted Fusion Drive




diskutil cs list
CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group CF679B40-3999-4A00-AA41-4D7CC546FB41
    =========================================================
    Name:         Macintosh HD
    Status:       Online
    Size:         722905776128 B (722.9 GB)
    Free Space:   106496 B (106.5 KB)
    |
    +-&lt; Physical Volume BF1C586C-AECF-4640-90A3-EF1F1B1B1776
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk1s2
    |   Status:   Online
    |   Size:     23553724416 B (23.6 GB)
    |
    +-&lt; Physical Volume 7018B90D-8378-4015-A9F5-B531B325FABE
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     699352051712 B (699.4 GB)
    |
    +-&gt; Logical Volume Family 9AD3A7A0-D9E3-4A3F-B233-7EACB65C38BC
        ----------------------------------------------------------
        Encryption Type:         None
        |
        +-&gt; Logical Volume 9449131B-67F8-4D97-82D6-F2BDEDB48B6C
            ---------------------------------------------------
            Disk:                  disk2
            Status:                Online
            Size (Total):          722000936960 B (722.0 GB)
            Revertible:            No
            LV Name:               Macintosh HD
            Volume Name:           Macintosh HD
            Content Hint:          Apple_HFS
            LVG Type:              Fusion, Sparse
Your Windows partition isn't missing after erasing it! You gained some unallocated disk space. 

To reinstall Windows with Boot Camp Assistant you have to restore the ~vanilla Fusion Drive state. You can try to resize the whole Core Storage stack with the command with: diskutil cs resizeStack lvUUID size. In your case that's: 

diskutil cs resizeStack 9449131B-67F8-4D97-82D6-F2BDEDB48B6C 1022g


If you get an error "... not enough space ..." choose a slightly smaller size like 1021500m or 1021g.

After poking around with Disk Utility or the Windows Disk Management tool (e.g. trying to remove/resize a Boot Camp partition with Disk Utility) the resizeStack command often fails with a cryptic -8xxxx error message because some internal CoreStorage structures are corrupted. Your OS X volume usually isn't affected though.

Then you have to either backup the OS X partition with Time Machine, rebuild a vanilla Fusion Drive and finally restore the TM backup or install OS X from scratch after rebuilding a vanilla Fusion Drive.

Then you can launch Boot Camp Assistant and install Windows 10 again.