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Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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I want to change the SSD of my Fusion drive

I want to check the size of the SSD part of my Fusion Drive and if it makes sense to install a bigger SSD.

I have a 3TB Fusion Drive and I suppose there is an 128GB SSD installed.

Does it make sense to put in a 500 GB SSD as I have one left from upgrading my MacBook Air.

And is there any diskutil procedure or repair mode action necessary to bind these drives together again or can I just flip the SSDs?

Thank you very much.

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Yes your system has a custom 128 blade SSD for the Fusion Drive.

Sadly, you can't reuse your MacBook Air's SSD in your iMac. Review this great guide on Apples SSD's The Ultimate Guide to Apple’s Proprietary SSDs.

You need to break the Fusion Drive set before altering it and then re-enable it using a set of terminal commands.

Please tell us why you want to alter your Fusion Drive set.


Dear Dan

Why can't I reuse my MacBook Air's SSD? Different standard? Or because of the necessary rebuild of the Fusion Drive?

I wanted to reuse my SSD from my MacBook Air. That was the reason I asked. If it would make a difference of course. But id 128GB are enough and the performance could not be improved then I abstain...

Thank you very much!


The systems used different sized blade drives. The 500 GB drive is physically too big. Did you review the guide?


But does it make sense to install a bigger SSD as part of the Fusion Drive?

{When it’s the proper model of course}


Frankly if you had a workable 500 GB SSD I would setup a dual drive config and not bother with a Fusion Drive setup. Here the SSD would be your boot drive with your OS & Apps. Your HDD would then hold your data and created work.


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1 Answer

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Lets first look at why Apple intro’ed the Fusion Drive: At the time SSD’s where very expensive but wicked fast over slow HDD’s. People wanted both the deep storage of an HDD and the speed of an SSD.

Both Seagate & Western Digital saw this and responded with two competing designs (hybrid drives - SSHD). Seagate offered a HDD with a SSD cache unit and WD offered a dual drive sandwiching a HDD & SSD into one device! Apple wanted to leverage their blade SSD development and copied the Seagate concept. But, unlike Seagate, Apple leveraged a faster PCIe interface its blade drives offered and handled the caching within the OS instead of within the drive unit. Fusion Drives where born!

Lets jump forward back to today, the cost of nonproprietary 128 GB was pushing $200 back in 2011 today a 1 TB is less than $200! Sadly, proprietary SSD’s have not fallen as far as commodity drives.

So today Fusion Drives are not needed for the same reasons and if someone does their research in buying a new system they would not buy it. Instead they would spend the money on getting a straight SSD system to gain the speed and get a large enough drive to support the applications and scratch space needed for the tasks the system was bought for.

In your case the question then becomes a question of risks in opening the system to even get to the blade SSD and as Apple is using a proprietary SSD design. Then the higher cost of the proprietary drive Vs using an external RAIDed SSD Thunderbolt drive, or just replacing the SATA HDD to a SSD.

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Thank you very much! Much appreciated


Dear Dan

If I would decide to change the fusion drive pro an SSD only drive do I have to remove the SSD part of the Fusion drive too?

Or do I have to expect a beep of some kind if I do that?


Required steps:

● Backup your data!

How to split up a Fusion Drive

● Remove the desired drive SATA HDD 3.5" drive and/or PCIe SSD blade drive

iMac Intel 27" EMC 2546 Hard Drive Replacement

iMac Intel 27" EMC 2546 Blade SSD Replacement

You don't need to remove the blade SSD if you only want to replace the HDD

● Setup the blade SSD as your boot & app drive - Format & install OS - APFS

◆ Leave the rest of the drive empty! Ideally 1/3 for a 128 GB, 1/4 for a 512 GB/1 TB

● Setup the SATA drive as your data drive - Format - HFS+ if HDD, APFS if SSD


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