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Model A1419 / EMC 3070 / Mid 2017 / 3.4, 3.5 or 3.8 GHz Core i5 or 4.2 GHz Core i7 Kaby Lake Processor (ID iMac18,3) / Retina 5K display. Refer to the older iMac Intel 27" Retina 5K Display (Late 2014 & 2015) guides as the system is very similar.

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Is an HDD required?


I discovered the HDD in my Fusion Drive 27" 2017 iMac was dying/more-or-less dead, and decided to try my hand at using an OWC Aura kit to upgrade the iMac.

I split the Fusion drive and then disassembled the iMac. I've inserted the new OWC Aura drive (2TB to replace the 128GB that came with the iMac), and done most of the re-assembly.

However, before I close it back up with the adhesive, I'm unclear on one thing: if I leave the HDD bay empty and the SATA cable unattached, will the iMac work correctly with just the SSD inside?

It would be annoying to close the iMac up and then find that it won't run properly, so if I need to buy a replacement HDD to install, it would be good to know that first.

Thanks in advance,


Update (03/18/23)

As a follow up, I notice from this OWC video ( that when they add in a replacement HDD they use a new SATA connector with a temperature sensor, which isn't present with the drive that came with the iMac. If I do have to install a replacement HDD, do I need to get a new SATA connector with a temperature sensor?

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You do not need the HDD, it can be removed altogether, and furthermore my understanding is that the current versions of firmware for iMacs negate the need for the temp sensors of old. I have done several many upgrades of this sort in the last few years and never had an issue. Either replacing the HDD with an SSD or a non OEM HDD. Or removing one from a device that used to have one and installed an Apple blade instead.

They are much more flexible than they used to be in this regard. And with a 2 TB OWC drive, having the HDD is probably negligible, that's plenty of storage.

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Thanks Alisha. Just so I'm clear, are you saying that if I did put in a HDD for the longer time file storage (photos take a lot of space when you've been taking lots of them) and kept the SSD blade for the macOS and apps, I wouldn't need to get the temperature sensor for the third party HDD?


@andrewnz34074 Yes. Based on my experience anyways. So long as you’re running a relatively new version of macOS (which would come with newer firmware for your machine). I have personally installed SSDs in these without the thermal sensor and had no issues.

I also yanked the HDD out of a 2013 and swapped in a spare blade SSD we had lying around so I could have a second machine on my bench for when my Mac mini was inaccessible. Worked like a charm, no modifications even.


Thanks Alisha, that's helpful.


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To clarify things you system can run with a blade SSD alone but you need to use the newer macOS’s as Mojave and older don’t have the newer drive driver which supports the newer SMART spec. So you shouldn’t need the external sensor. Even still there is a special header which Apple installed on their systems HD power connection port which where blade SSD only systems.

I haven’t personally setup this series with a blade SSD only, I tend to setup dual drive systems or just upgrade the SATA drive to a SSD only.

To make your own header get a LP4 cable like this one

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Trim off the Red and Yellow wires (power) cutting the black wires so you can short the wires together is all that’s needed (ground) and plug in in where the HD power cable is connected. For the few bucks it’s worth the effort.

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Hi Dan, thanks for your answer.

I'm a bit confused by your reference to a header though, as it's a term I've not heard before. Are you saying that if I do go down the route of adding in a HDD (for the deeper, long term file storage) and kept the SSD blade for the macOS and apps, I could avoid buying the OWC cable with the temperature sensor and make one as you've described?

Or that if I don't add an HDD back into the iMac, I should make one of these header cables so the iMac's power and data (SATA) that used to plug into the HDD instead has this plugged into it so that there isn't a live cable 'floating around' inside the resealed iMac?

Much appreciated.


@andrewnz34074 - A header is the term used to describe the connector interface on the logic board. When you disconnect the HD cable assembly you will see there are two connections one is power the other is data.

The reason I would put it in is to comply with what Apple does with blade SSD only systems. And I just not sure if the lack of the connection will be an issue as I’ve not done a blade only setup in this series.


Many thanks Dan. I'm still thinking about whether to add an HDD back in, but if I don't that's good to know.


@andrewnz34074 - if you keep the HDD, I strongly recommend you make a full TimeMachine backup and reformat your drive, then restore the user account and Apps to the SSD, then restore again to the HDD with your stuff.


Yes, I've got TimeMachine and Carbon Copy Cloner backups of the former fusion drive. The old HDD is a write-off, But I'm not sure about the data integrity of those backups, so I'm going to be doing the OS and apps as clean installs and carefully copying back what files I can after that.


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AndrewNZ zal eeuwig dankbaar zijn.

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