I am having trouble after replacing my iMac's SuperDrive with a Solid State Drive (SSD).

I kept the original Hard Disk Drive (HDD) in place. I configured the SDD as the main startup disk and I transferred all the libraries in HDD.

The malfunction is that in the process of rebooting the iMac turns off.

Booting into safe mode the Disk Utility shows the new SSD drive is full, although before rebooting it has used only 90GB out of 480GB. I do the same procedure again, clean install of macOS 10.12, and again the same problem. Any ideas please for solution of this malfunction?

I have to say that if I do not reboot the iMac, it runs excellently, and the SSD drive has the same empty capacity 90GB used out of 480GB.

iMac 21" 2009/late. SSD Kingston 480Gb / macOS 10.12, Sierra.

2 Answers 2


I configured the SDD as the main startup disk and I transferred all the libraries in HDD.

How exactly did you transfer the libraries?!
Note, that Disk Utility.app (if used) does not create a bootable HDD backup!

There are different ways to clone/transfer the entire content of your previous installed main HDD. The following applications will allow exact and bootable drives/disk images.

Option 01: Carbon Cloner creates a bootable drive/volume

enter image description here

Option 02: CloneX4 allows you to make a bootable copy of your startup disk, as well as if you want to change your hard disk. Clone X will create a perfect bootable copy of your startup disk, or of any of your other disks. Clone X automatically handles all settings needed to make a correct bootable copy.

enter image description here


The problem here is that you can't just "transfer libraries;" you have to do one of the following:

  • Clone your drive (not recommended in this scenario as it's not a disaster recovery situation)
  • Install macOS and migrate your apps and data.

I much prefer the latter.

To do this, you are going to need a USB installer or you could do macOS Recovery by pressing CommandR (or CommandOptionR for Internet Recovery)

Using Disk Utility, make sure you wipe the drive and ensure there's only one partition so you can use the whole 480GB, then proceed to install on the SSD.

Once compete, use Migration Assistant to move your data from your old HDD to your new SSD. Just select the option that allows you to restore from another disk

enter image description here

Finally, since you are moving from an iMac that had a HDD to one that now has an SSD, make sure you enable TRIM support with the command sudo trimforce enable

  • Actually cloning your drive is preferred and easier: you get an exact copy of a working system on another (presumably larger) drive and don't have to do anything else except perhaps re-register some commercial software. I would only do an install and migrate if there were specific problems with the old system. Cloning is easier and quicker! Commented Mar 22, 2017 at 14:59
  • @SteveChambers - not so. Easier is not always better. Cloning works great if both drives are identical. If the are different sizes, you have the issue of lost space or lost data. You either have to repartition or do a lot of extra work for recovery. That said, cloning requires either advanced skills recovery mode then use dd` or purchase of software. My solution requires neither.
    – Allan
    Commented Mar 22, 2017 at 15:07
  • WRONG! Ghost, SuperDuper, ChronoSync, CCC will clone a small HD to a bigger one leaving you with all that lovely extra space ready to doe. Done it may times. Don't know where you get your info but mine comes from 25+ years of Mac IT work. Commented Mar 23, 2017 at 20:21
  • @SteveChambers ANYTHING will go from smaller to larger including the free dd. Did you read my whole comment? However, how do you know that the OP isn't going from larger to smaller? If I'm not mistaken those models came with .5TB with a 1TB as an option. Again, my solution is free, clean and stable - you don't have to buy a single piece of software.
    – Allan
    Commented Mar 23, 2017 at 21:11

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