is an apple fusion hdd physically separate from its ssd?

Question

is an apple fusion hdd physically separate from its ssd?

I have a 2013 21.5" iMac with a 1TB Fusion drive, it's working fine and I have no reason to buy a new one.

Current HDD usage is just over 556GB but I only have a 650GB backup disk and it won't be long before it's too small.

I could buy a larger backup drive but since the cost of a SSD is within my budget I'm considering buying a 1TB SSD to replace the Mac internal drive but need to know if the Fusion drive is physically two separate items or is the SSD part incorporated into the HDD, i.e., are HDD and SSD one physical thing?

My plan is to Install a 1TB SSD in the Mac and use the drive I remove from the Mac as my new backup drive.

So, if I do that and the removed drive has SSD built in, is that going to be a problem? Can I make use of that SSD or will it just sit there and do nothing?

Or, if the Fusion SSD is physically separate from its HDD, what happens to it if I install the 1TB SSD? Is the Fusion SSD still available in the Mac to make it and the new 1TB SSD a Fusion drive?

Thanks,

Davo.

iMac (21.5-inch, Late 2013), macOS Sierra (10.12.6), 16GB Memory

Posted on Jan 13, 2018 9:29 PM

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Answer 1

Top-ranking reply

samtenor

Level 4

2,074 points

Jan 14, 2018 6:38 AM in response to davofromulladulla

The fusion drive is "physically" 2 drives: a PCI-e (blade shape) SSD (usually small, like 64GB 128GB..etc, depends on the configuration of the year/models), and 1 HDD (usually 1T 2T etc).

Fusion drive is using a software control command to "fuse" two drives into ONE DRIVE for the system to recognize its existence. Therefore, both drives carried some commands within for the OS during booting/operating. That been said, in the event of "HDD failure" or "removal of HDD" -- it will cause some issues.

In your case, to replace the HDD with SSD -- there are few steps to take to avoid headaches.

1. Backups (even multiple backups) of your current system.

2. Make sure your SSD has up-to-date firmware from the vendor, then "erase" it with Apple GUID format

3. Make a bootable USB OS (this will make your life easier) Google search, you will find "how to" make a bootable USB drive of your desired OS version.

4. the tools you might need for the tasks (ifixit carries a wonderful "pizza like" cutter to cut the seal between the chasis and the glass) (reseal tape) with OWC video guide etc. -- and a pair of steady hands

5. Boot up from the USB drive by using "option" key

6. Under "Disk Utility" - you have to rebuild a fusion drive (that been said, your PCI-e SSD will be erased to be associated with your new drive)

How to fix a split Fusion Drive - Apple Support

7. Install OS then restore your system

8. You might want to check "TRIM" since your 1T SSD is third party. You can go to "about this Mac" -->"system report"

--> SATA/SATA express to see the link speed, TRIM support and SMART

Good luck

Sam

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Answer 2

Jan 15, 2018 12:05 AM in response to samtenor

Hi Sam, Many thanks for your reply.

It looks eminently do-able, just a bit of work is all.

I take it that the "How to fix a split Fusion Drive - Apple Support" link instructions are to be followed as part of step 6?

The link instructions say to use Terminal to enter commands.

Can you please clarify step 6 for me, I don't want to screw anything up.

I've checked my current system (Apple SSD 128GB) to have a look at the Trim Support, it's there but I haven't got a clue what that means - I can't see any reference to a link speed (possibly because my Fusion Drive is split into two drives and it's not a Fusion anymore). SMART status is verified.

Is there a danger of Trim being absent or unusable or something if I use a third party SSD replacement for the HDD? If so, what are the pros and cons of having/not having it?

Thanks again,

Davo.

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Answer 3

samtenor

Level 4

2,074 points

Jan 15, 2018 2:04 PM in response to davofromulladulla

Hi Davo:

if for iMac 21.5 inch, the drive size is 2.5 -- therefore, you do not need any adapter like 27" iMac.

As soon as you remove the HDD, the internal PCI-e SSD will be likely non-functional. That is why "making a USB boot drive" to be essential to build a new Fusion drive.

I am attaching a new link:

https://www.macworld.com/article/2014011/storage-drives/how-to-make-your-own-fus ion-drive.html

You will have to treat the existing PCI-e SSD as new one -- because rebuilding a new Fusion drive, you will loose all the data on it (that's why backup backup and more backup!).

The whole process is to build a unique UUID for CoreStorage (Fusion drive).

TRIM is important for SSD (life expectancy) and since your fusion drive will be composed with Apple OEM PCI-e SSD with 3rd party SSD. The third party SSD will NOT be TRIM enabled natively like Apple's OEM SSD. Therefore, after the OS is loaded, system is operational, you might want to check TRIM for the 1T drive. There is a terminal command: sudo trimforce enable --- again, you will see all "warning" from Apple and it will be your own risk.

https://en.wikipedia.org/wiki/Trim_(computing)

Good luck

Sam

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Answer 4

Jan 15, 2018 12:21 AM in response to samtenor

Sam,

I forgot to ask, is the internal HDD a 2.5" or a 3.5" - it's in a 2013 21.5" iMac, I think it's 2.5" but want to make sure.

Thanks again.

Davo.

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Answer 5

Jan 15, 2018 2:44 PM in response to samtenor

Thanks, Sam,

I'm holding off doing this for a while so I'll archive all the info you provided.

Many thanks,

Davo.

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