Missing space on Fusion Drive (partition problem) I know this or similar problems have been discussed, but (to be honest) I can't see the trees for the wood. 
I tried to create a partition on my fusion drive (1TB Hd + 240 MB SSD). No partition was created but afterwards the capacity of my (1.2 TB) drive had been reduced to 617 GB. With 414 GB in use, approximately 400 GB of disk space is missing.





Terminal diskutil list says: 

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 myLogicalVolGroup       999.3 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *240.1 GB   disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage myLogicalVolGroup       239.7 GB   disk1s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk1s3
/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS HD IMac 1              +616.6 GB   disk2
                                 Logical Volume on disk0s2, disk1s2
                                 7EE2FE6D-3D37-46AA-B948-52243490F324
                                 Unencrypted Fusion Drive


and: 

diskutil cs list
CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group 53DFB831-BFCA-4552-A8F5-387F3905003A
    =========================================================
    Name:         myLogicalVolGroup
    Status:       Online
    Size:         1239058563072 B (1.2 TB)
    Free Space:   615951769600 B (616.0 GB)
    |
    +-&lt; Physical Volume A1418DDB-CB43-493F-9341-F23AE2FA7150
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     999345127424 B (999.3 GB)
    |
    +-&lt; Physical Volume 2E45A45F-D1C1-4B62-97FA-5223DD9C965E
    |   ----------------------------------------------------
    |   Index:    1
    |   Disk:     disk1s2
    |   Status:   Online
    |   Size:     239713435648 B (239.7 GB)
    |
    +-&gt; Logical Volume Family E3B8F7DC-C327-44A7-8BE2-2BFD2AE646EB
        ----------------------------------------------------------
        Encryption Type:         None
        |
        +-&gt; Logical Volume 7EE2FE6D-3D37-46AA-B948-52243490F324
            ---------------------------------------------------
            Disk:                  disk2
            Status:                Online
            Size (Total):          616601616384 B (616.6 GB)
            Revertible:            No
            LV Name:               HD IMac 1
            Volume Name:           HD IMac 1
            Content Hint:          Apple_HFS
            LVG Type:              Fusion, Sparse


Would this simply be a matter of:

diskutil cs resizeStack 7EE2FE6D-3D37-46AA-B948-52243490F324 0g  (?)


Hope some-one can help me with this.
Starting with OS X 10.11 (El Capitan) you'd have to enter a distinctive (> 0) size to execute the resizeStack command. The magical ... 0g doesn't work anymore.

But in your case the resizeStack option is the wrong one because your Logical Volume Group already occupies almost all available space on the Fusion Drive:

Total disk space: 1240 GB
LVG size:             1239 GB
PV1 + PV2 size:   1239 GB
LV size:                  616 GB

The resizeStack option is appropriate if you want to resize the LVG and all subsequent Core Storage items (like the LV, PV and LVF).

Here you just have to expand your Logical Volume to completely fill the LVG with the following command:

diskutil cs resizeVolume lvUUID size


In your case that is:

diskutil cs resizeVolume 7EE2FE6D-3D37-46AA-B948-52243490F324 1239g


If you get an error (not enough space...) choose a slightly smaller size like 1238g.



After further investigations one have to state that the Fusion Drive is corrupted:

Boot to Internet Recovery Mode, destroy the LVG, rebuild the Fusion Drive and restore your Time Machine backup: here is a how-to. Start with 'Rebuild Fusion Drive' (recommended if you have a Time Machine backup).