Merge Primary Partition with Free Space – Disk Utility Guide

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I used to have only a 500gb SSD for my MacBook Pro, but later came across a 1TB SSD that I wanted to switch to using. Instead of using the 'recommended' method, I opted for the dirty route and just connected another MBP in Target Disk Mode via Thunderbolt and used pv /dev/rdisk0 > /dev/rdisk(x) x = whichever disk for the 1TB at the time.

However, prior to copying the entire contents over to the 1TB SSD, I used rEFInd and installed a copy of Kali Linux as a dual boot, which I've been running with…..minimal issues for quite some time now.

So the 'dirty' copy worked as planned, the 1TB SSD boots fine and, after a quick reinstallation of rEFInd, everything runs perfectly as it ever has – except now I have an additional 500gb of 'Free Space' at the very end of the 1TB SSD.

I've tried booting to an external OS X drive and using Disk Utility (both from Yosemite Disk Utility and El Capitan Disk Utility), to expand/merge/delete/create anything to do with this 'Free Space' – without any working results.

So my question is: how can I reclaim this 500gb of space at the END of my 1TB SSD, without compromising any of the other partitions (including primary OS X, Recovery, rEFInd, Kali Linux & Linux Swap), and merge it with my primary partition so I can actually use this space?

Here are some visuals of my partition layout and other various info to help see what I mean…

Disk Utility Yosemite

Disk Utility El Capitan

diskutil list

Best Answer

If you hesitate to dd partitions or backup and restore your data with Time Machine, you may convert the first OS X partition of your disk to a Physical Volume and create a Logical Volume Group. After creating a second partition in the free space you can add it to your LVG and expand your current Logical Volume.

The approach is similar to a Fusion Drive (two Physical Volumes -> one Logical Volume Group/Logical Volume) however using only one disk.

  • Boot to Macintosh HD
  • Attach a backup drive and use Time Machine to backup Macintosh HD.
  • Detach the backup drive
  • Open Disk Utility and add a JHFS+ partition in the free space (~500 GB)
  • Enter diskutil list to list all partitions
  • Enter diskutil cs convert /dev/disk0s2 to convert your main volume to CoreStorage
  • Enter diskutil cs list to get all CoreStorage items

  • Enter diskutil cs addDisk lvgUUID diskYsZ to add the new empty 500 GB partition as Physical Volume to the Logical Volume Group.

    lvgUUID is the UUID of the Logical Volume Group, diskYsZ is the disk identifier of the empty partition 500 GB partition (probably disk0s6). The content of the partition will be destroyed!

  • Enter diskutil cs resizeVolume lvUUID size to extend Macintosh HD.

    lvUUID is the UUID of the Logical Volume, size: size in t, g, m, k or b (in your case ~850g. If you get an error regarding missing space use a slightly smaller size like 849g).

  • Enter diskutil verifyDisk disk0 and diskutil verifyVolume disk0s2.

The pros:

it's fast; it takes about 3 minutes.

The cons:

your CoreStorage LVG is non-contiguous and "fragmented".

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