MacOS – How to merge System partition with another HFS+ partition without data loss

disk-utilityhard drivemacospartition

My hard drive is split in three visible partitions: System, Data and Backup.
I'd like to merge System (OS X Lion) and Data into one partition without data loss.

Disk Utility won't let me resize the system partition:

partitions in disk utility

That's my complete setup:

enter image description here

Apparently, I can't use mergePartitions because diskutil man says:

mergePartitions [force] format name fromDevice toDevice

Merge two or more partitions on a disk.
All data on merged partitions other than the first will be lost.

I can imagine decreasing Data size, creating a New partition, moving all files from Data to New and proceeding with mergePartitions, thus merging System and Data into System+Data. Then I probably can move stuff from New to the merged System+Data partition and merge them all.

However I'm unsure what will happen to Recovery HD that stands between System and Data. Will it get erased? If so, how can I restore it?

Best Answer

There is absolutely no way that you should even think about doing any of this without a complete backup on a separate disk. Verify the backup before beginning.

1) If you have a complete backup, the easiest way to do this would be to wipe everything, make the partitions you want, and then copy the information back from your backup. If your Recovery HD is deleted, there is no way to re-create it without reinstalling the OS. (At least none that I could find when I was searching recently.)

2) Assuming you have a backup OTHER than that Backup partition, if you want to attempt to merge these, I would try it in this order:

a. Delete the 'Backup' partition.

b. Merge 'Data' partition and former 'Backup' partition.

c. Merge System partition and other partition.

d. Re-create the 'Backup' partition and restore it from whatever backup you have.

I have done several live-system partition resizings with no problems. However, the one time that there was a problem, I had to reformat the entire drive and start over.

Related Solutions

MacOS – Resizing or expanding a CoreStorage volume

After gaining some experience with CoreStorage volumes, I reworked my first answer to generalize and facilitate it by adding some scenarios and deleting some dispensable steps.

Basically there is one undocumented command to resize or expand a CoreStorage volume group and an inherent logical volume:

diskutil cs resizeStack LVUUID size

The command expands or shrinks the whole CoreStorage Volume Group including the physical volume(s), the logical volume family and the logical volume in one step to the desired size.

While shrinking it down to the size of the occupied space in the logical volume shouldn't be problem at all (but not recommended because at least 10% free space should be left), any blocking partition except the recovery partition has to be deleted or diminished before expanding the CoreStorage stack.

The command comes in handy in several scenarios:

expanding a CoreStorage volume after deleting a 2nd old-style JHFS+ volume on the same device (this may happen after splitting your disk in two partitions in Mavericks and then updating to Yosemite. The first partition - your system volume - might be converted to a CoreStorage volume, while the 2nd volume is left alone.)

enter image description here

expanding a CoreStorage volume after manually deleting a Boot Camp NTFS volume

enter image description here

resizing a CoreStorage volume to create 2nd old-style JHFS+ volume on the same device

enter image description here

Beware: The command is vastly undocumented and as such potentially destructive.

Preparation:

Backup your data.
Detach any external drive (especially your external Time Machine backup drive).
Restart to Internet Recovery Mode by pressing alt cmd R at startup.
The prerequisites are the latest firmware update installed, either ethernet or WLAN (WPA/WPA2) and a router with DHCP activated.
On a 50 Mbps-line it takes about 4 min (presenting a small animated globe) to boot to a recovery netboot image which usually is loaded from an apple/akamai server.

I recommend ethernet because it's more reliable. If you are restricted to WIFI and the boot process fails, just restart your Mac until you succeed booting.

Alternatively you may start from a bootable installer thumb drive (Mavericks or Yosemite) or a thumb drive containing a full system (Mavericks or Yosemite).

Modify CoreStorage stack:

Open in the menubar Utilities/Terminal

First you should get an overview of your disks and the partition layout:

Enter diskutil list
Example listing:

/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *68.7 GB    disk0
   1:                        EFI EFI                    209.7 MB    disk0s1
   2:          Apple_CoreStorage                         53.7 GB    disk0s2
   3:                 Apple_Boot Recovery HD            650.0 MB    disk0s3
   4:                        EFI No Name EFI            100.0 MB    disk0s4
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                         *1.3 GB    disk1
   1:        Apple_partition_map                         30.7 KB    disk1s1
   2:                  Apple_HFS OS X Base System        *1.3 GB    disk1s2
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS System                 *53.5 GB    disk2
/dev/disk3-disk12 ...belong to the OS X Base System (your recovery system you booted to previously)

Disk0 is your main internal disk device containing the EFI-partition (dis0s1), the CoreStorage partition (disk0s2) and the Recovery HD (disk0s3). The No Name EFI (disk0s4) only exists if you had a Boot Camp partition previously and deleted it manually.

Disk1 is a logical disk created by booting to the netboot image which contains a recovery system (OS X Base System = disk1s2) similar to the Recovery HD.

Disk2 is also a logical disk residing in disk0s2 and it contains the CoreStorage stack.

Enter gpt -r -vv show /dev/disk0
Example listing:

gpt show: /dev/disk0: mediasize=68719476736; sectorsize=512; blocks=134217728
gpt show: /dev/disk0: PMBR at sector 0
gpt show: /dev/disk0: Pri GPT at sector 1
gpt show: /dev/disk0: Sec GPT at sector 134217727
      start       size  index  contents
          0          1         PMBR
          1          1         Pri GPT header
          2         32         Pri GPT table
         34          6         
         40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
     409640  104974016      2  GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
  105383656    1269536      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
  106653192     204800      4  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
  106857992   27359703         
  134217695         32         Sec GPT table
  134217727          1         Sec GPT header

The partition with the index number 1 is the regular EFI-partition, the partition with index number 2 is your CoreStorage partition and the partition with index number 3 is your Recovery HD.
The partition with index number 4 (=No Name EFI) only exists if you had a Boot Camp partition previously and deleted it manually. All the rest is unallocated free space (in the example 27359703 blocks à 512 B).

Enter diskutil cs list
Example listing:

  CoreStorage logical volume groups (1 found)
|
+-- Logical Volume Group A629E051-D7B0-4B8C-A803-074F62704636
    =========================================================
    Name:         System
    Status:       Online
    Size:         53946696192 B (53.9 GB)
    Free Space:   16777216 B (16.8 MB)
    |
    +-< Physical Volume 90C09FC0-4215-4871-901B-70E2C9C7D464
    |   ----------------------------------------------------
    |   Index:    0
    |   Disk:     disk0s2
    |   Status:   Online
    |   Size:     53946696192 B (53.9 GB)
    |
    +-> Logical Volume Family F6962E38-50E4-4458-BFE6-CF2E179352F5
        ----------------------------------------------------------
        Encryption Status:       Unlocked
        Encryption Type:         None
        Conversion Status:       NoConversion
        Conversion Direction:    -none-
        Has Encrypted Extents:   No
        Fully Secure:            No
        Passphrase Required:     No
        |
        +-> Logical Volume BD36C73D-860D-4DC6-B125-AD624F448B88
            ---------------------------------------------------
            Disk:                  disk2
            Status:                Online
            Size (Total):          53496696192 B (53.5 GB)
            Conversion Progress:   -none-
            Revertible:            Yes (no decryption required)
            LV Name:               System
            Volume Name:           System
            Content Hint:          Apple_HFS

to resize the CoreStorage volume you have to delete any blocking partition first (the Recovery HD doesn't count because it usually will be moved with the resizeStack command).
First you have to unmount all mounted volumes on disk0 (first the CoreStorage volume, which has its own disk identifier disk2 but resides on disk0, then all other mounted volumes on disk0 - check this with df):
```
diskutil unmountDisk /dev/disk2
```
then additional volumes (if you have any at all). Example:
```
diskutil unmount /dev/disk0s5 
```
If you have a NoName EFI partition delete it by entering:
```
gpt remove -i 4 disk0
```
Remount any previously unmounted volume in the reverse order with
```
diskutil mount /dev/disk0s5
diskutil mount /dev/disk2 
```
Since any blocking partition is deleted you may now resize the CoreStorage volume with
```
diskutil cs resizeStack LVUUID size 
```
with LVUUID: UUID of the logical volume and size: the final size of your CoreStorage volume.
Examples:
```
diskutil cs resizeStack BD36C73D-860D-4DC6-B125-AD624F448B88 60g  
```
to expand it to 60 GB
```
diskutil cs resizeStack BD36C73D-860D-4DC6-B125-AD624F448B88 40g  
```
to shrink it to 40 GB
```
diskutil cs resizeStack BD36C73D-860D-4DC6-B125-AD624F448B88 0g 
```
to expand it to the full available size (0g is a magic number here).

Your Recovery HD should be moved automatically - regardless of whether shrinking or expanding the CS volume - to the very end of it.
In case of shrinking the CoreStorage volume you may now create a 2nd partition with gpt.
Enter the following to get the new partition scheme:
```
gpt -r -vv show /dev/disk0
```
and
```
gpt add -b StartBlock -s NumberOfBlocks disk0
```
to create a new partition. StartBlock is the number of the first block in the unallocated space and NumberOfBlocks is the number of free blocks or smaller. NumberOfBlocks has to be dividable through 8!
Enter exit and quit Terminal.
Open Disk Utility (and format your newly created partition if you have created a new partition in the second last step).
Then check your expanded CoreStorage volume for errors.
Quit Disk Utility.
Reboot to your main volume.

MacOS – How to create a new partition for OS X, then remove the original one

With Apple's OS X tools you can't expand the start sector of a partition to lower sector numbers. You have to choose another method.

You may accomplish your objective if less then one half of the net capacity of your hard drive ((~disk size - size of Recovery HD - size of EFI)/2) or less then one half of the main volume is occupied. If you miss the threshold narrowly you may remove swap files, sleepimage and clean the temp folders to lose further GBs.

In this particular case you may add a second volume with the same size as your then narrowed previous main volume, which is equivalent to splitting the available space in two equal volumes (with the first volume still containing your old OS X installation).

After installing your new OS X to the new volume ("El Capitan") you may transfer your apps, settings and data to the new volume.

After migrating your stuff you have to delete the old CoreStorage Logical Volume Group (the superior Macintosh HD) with:

diskutil cs delete lvgUUID

with lvgUUID: UUID of the Logical Volume Group. To get the lvgUUID use:

diskutil cs list

Deleting the Logical Volume Group will automatically create one new classical JHFS+ volume with the name "Untitled" occupying all available space on the disk.

Now clone your new volume "El Capitan" to the empty volume "Untitled" with an appropriate tool (Disk Utility/Carbon Copy CLoner). The former "Untitled" will be renamed to "El Capitan". So rename the former "El Capitan" to "El Capitan_Old"

After successfully booting from "El Capitan", delete "El Capitan_Old" with Disk Utility and expand "El Capitan" to the full available size of your disk.

If more than one half of your (old) main volume is occupied you need an external disk to migrate or you have to delete some data.

Best Answer

Related Solutions

MacOS – Resizing or expanding a CoreStorage volume

MacOS – How to create a new partition for OS X, then remove the original one

Related Question