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I have got an iMac (EMC 2638) here, with 1TB hard drive. I have read that there is a PCIe SSD slot on those iMacs as well, originally for the fusion drive. Is it possible to upgrade my iMac with such a SSD module? I don't care if it would work as a fusion drive, or simply have it as the main drive for OS and programs.

If this is possible, where can I buy such a SSD module? iFixit has repair instructions, but maybe I can let this be done by my local Mac shop.

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It seems there is a workaround for this. One can buy an external Thunderbolt SSD, and set up a Fusion Drive. Since Thunderbolt is extremely fast, this is a low cost, low work solution that is very suitable for desktop machines like the iMac.

There are a lot of guides online on how to set up the disks.

It boils down to

  1. Backing up your machine using Time Machine
  2. Install OS X onto a third external drive.
  3. Boot from said drive.
  4. Create fusion drive over external SSD and internal HD.
  5. Reboot from fusion drive and re-install OS X, restore from Time Machine

Maybe one can skip the install to external HD, since newer Macs come with Internet Recovery. This would save quite a bit of work.

Once in recovery, you can see your disks using diskutil list. Let's say you see the disks disk1s2 (internal HD, OS X partition) and disk2 (clean SDD).

Now you can create the Fusion Drive:

sudo diskutil cs create [ArbitraryName] disk2 disk1s2
sudo diskutil cs createVolume [UUID] jhfs+ [ArbitraryName] 100%

The output of the first command results in a UUID which you use in the second command.

After this, you should be able re-install or restore OS X onto the Fusion Drive.

I haven't tried this yet, it is merely a summary of the linked article! So be careful and make backups!

  • I often wish someone brought Thunderbolt thumb drives to the market. They'd be scary fast. – Patrick McMahon Jan 13 '15 at 16:01
  • That'd be a great idea. For an upgrade fusion drive, 64GB would probbly be enough. Ose could probably be manfuctured with rather rather small cases. – Arne Jan 13 '15 at 18:27

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