2017 iMac 4K Retina (A1418 / 18,2) upgrade - Fusion Drive and RAM

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Tony-P Author

Level 1

11 points

2017 iMac 4K Retina (A1418 / 18,2) upgrade - Fusion Drive and RAM

Hello Apple Community:

I have 2 questions about my 2017 iMac 4K Retina (A1418 / 18,2):

How can I upgrade the “Fusion Drive” on a 2017 iMac (A1418 / 18,2) quad core i5 with a 4K Retina display to a higher overall storage capacity?
Can this iMac’s RAM be upgraded from 8GB to 32 GB?

Some background:

I am aware of and prepared to tackle the technical challenges in opening and modifying this particular generation of iMacs, so I am specifically asking about the mechanics of replacing the Fusion Drive.

My understanding of the Fusion Drive is that it consists of a Solid State Drive (SSD) component and a traditional (spinning disk) Hard Disk Drive (HDD). I’ve been told that these 2 drives mirror each other and that the SSD handles the more frequently accessed system features with greater read/write speeds, whereas the HDD is used for less frequently accessed storage.

When I bought this iMac I thought was getting 2 TBs of total storage capacity. However, in more recent discussions with Senior AppleCare Tech Support Advisors, I am concluding that these 2 drives actually mirror each other, and that my maximum total / accessible storage is really only 1TB. Is this correct?

If the 2 drives in the iMac do mirror each other, does anyone know how this happens? Specifically, is this “RAID 0” system architecture or is there is some other way in which this mirroring takes place? From what little I know about RAID architecture, both components need to be of identical capacity. If this is true for this iMac, then what are my options for the upgrade I am planning?

Other questions: What hardware incompatibilities or issues could present themselves as part of this upgrade? This includes how to deal with the temperature sensor. Also, is upgrading the SSD component of the Fusion Drive limited to PCie-based components?

The question about the RAM upgrade is more straightforward: I’ve read that the factory-installed 8GB of RAM is user-replaceable. Is this correct? And if it is upgradable and what is the maximum amount of RAM this iMac will recognize? I have read the RAM maxes out at 32GB. Is this correct?

Any insights, advice or practical tips the Apple Community might have to share on the above questions would be greatly appreciated.

Thanks!

Tony-P

iMac, OS X 10.11

Posted on Mar 11, 2021 5:56 AM

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Answer 1

Top-ranking reply

padams35

Level 4

3,451 points

Mar 11, 2021 9:56 AM in response to Tony-P

Macintosh HD and Macintosh HD - Data are two partitions. They share the same 1.03TB (1TB HDD + 32GB SSD) logical drive.

(For a technical overview on APFS partition storage: https://developer.apple.com/documentation/foundation/file_system/about_apple_file_system)

For drive identities check the 'SATA' 'PCI' and 'NVMExpress' sections of system report.

Yes, you can replace the 1TB HDD with a 2TB SSD without worrying about the 32GB blade. This is the simplest upgrade and will double your storage but 2.5" SATA SSD drives are slower than the blade so while drive speeds will become more consistently quick peak speed may be somewhat slower.

Similarly you could replace the 32GB blade with a 2TB SSD without worrying about the HDD, but that uses a non-standard connector requiring either a custom made-for-2017-iMac SSD or an adapter.

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Answer 2

Tony-P Author

Level 1

11 points

Mar 11, 2021 8:15 AM in response to padams35

Hi Pandams35:

Thank you for the prompt reply and your interest in helping me think this through.

Putting the degree of difficulty involved in a RAM upgrade aside for the moment......

I'm just curious about whether the RAM soldered to the logic board or if it's installed in traditional DIMM slots? And is it correct that a max of 32GB can be recognized by this particular iMac?

Regarding the storage question: Is the 32GB SSD replaceable / upgradable (or would that serve no useful purpose, given that it is essentially operating as a cache?

Also - When I look at the System Report for Storage under "about this Mac" I see the following (please refer to the attached screen-shot)-

At the top of the screen-shot here are 2 volumes identified: Macintosh HD and Macintosh HD - Data. Are these simply 2 partitions on the same physical HDD? If so, does this mean that the actual total storage capacity of my HDD is 1TB?

If I replace the HDD with a 2TB SSD would I essential double my available storage and could I also improve my read-write speeds?

At the bottom of the screen-shot there is a Physical Drive identified as an SSD using a PCIe protocol. I am assuming that this is the 32GB Blade Drive. But why is the physical drive containing the 2 volumes at the top of the screen-shot not identified anywhere? Again, I am assuming this is an HDD. I'd just like to know a little bit more about it (brand, speed, etc.). Your thoughts?

Last question: Can I replace the 1TB HDD with a 2TD SSD without worrying at all about the 32GB blade SSD?

At a minimum, I'd like to try upgrading the storage, so I would appreciate any further insights or advice you may have about this and any replies to the different questions I've posed in this post.

Thanks, again!

Tony-P

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Answer 3

Tony-P Author

Level 1

11 points

Mar 14, 2021 12:22 PM in response to dialabrain

Thanks for the continued input and information.

Using an external Thunderbolt drive would be an option if both available Thunderbolt ports were not already in use. For better or worse, I have a lot of peripherals connected to this iMac and I'm using a pair of Thunderbolt to multi-USB plugs to attach them.

As I stated in my original post on this topic, I was told by the sales associate at the Apple Store that I was buying an iMac with a total of 2TB of storage in a part-HDD, part-SSD "Fusion Drive". So the prospect that I might only actually have 1.032TB of storage was really disappointing.

When I visited the OWC website to explore their menu of upgrade options available for my 18,2 iMac, their specifications list for my computer shows that the configuration I purchased IS supposed to include 1TB of SSD storage in addition to the 1TB HDD. Please look at the attached screen shot that includes the "About This Mac" window from my iMac.

I guess it's possible that OWC's website info could be incorrect. I just find it curious that the Apple Store sales representative would make the exact same mistake.

There's something else that isn't making sense to me so far:

Take a look at the attached side-by-side screen shots taken from the "SATA / SATA Express" , the "STORAGE" and the "NMVE express" sections of the System Report.

It appears that 3 different physical drives with 3 different BSD Names are listed.

Under STORAGE there is a 1.023 TB SSD (apparently connected using a PCI-Express "protocol" named "disk2s5". This drive appears to be holding all my data since only 89GB are free and under SATA / SATA Express there is a 1 TB 5400 RPM HDD named "disk0"

In addition to these two 1TB drives, under the tab "NVME Express" a second SSD is listed under the category heading "Apple SSD Controller" (identified as APPLE SSD SM0032L) with a BSD name "disk1". I am assuming that this is the 32GB "Blade" drive.

So, unless l am mistaken there actually are 2 distinct 1TB disk drives in addition to the 32GB Blade SSD drive. I have been told that the blade drive is functioning as a "cache". And since all my data is apparently being saved to the 1TB SSD (disk2s5) I am wondering what the 5400RPM HHD (disk0) is actually doing.

So - in terms of the approach to upgrading this iMac, the primary 1TB SSD appears to be connected via a PCIe slot (hopefully a removable drive and not soldered into the logic board) and the 5400 RPM HDD appears to be attached via a SATA connector.

The description of the NVME Express 32GB blade drive does not show a connector or connection-type (SATA or PCIe). Does that mean it is soldered to the logic board? And if it is specifically functioning as an "Apple SSD Controller" does it make any sense to try upgrading it anyway?

These questions all lead back to my earlier question about how the two 1TB disk drives work, how they interact with each other and what impact upgrading just one of these drives would have.

Any further thoughts, insights or comments would be greatly appreciated.

Thanks!

Tony-P

[Image Edited by Moderator to Remove Personal Information]

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Answer 4

padams35

Level 4

3,451 points

Mar 13, 2021 1:41 PM in response to Tony-P

You and the sales associate are mistaken.

Apple has never shipped an iMac configuration with both a 1TB SSD and a 1TB HDD.

A 1TB SSD was available as an option for build-to-order purchases for a +$500-700 premium, but that configuration shipped as SSD only without any HDD included.

OWC's info is correct. The configurations that Apple had available for purchase were:

> 1TB HDD only

> 1TB Fusion (1TB HDD + 32GB SSD) <---- This is what you have

> 256GB SSD only

> 512GB SSD only

> 1TB SSD only

The 32GB blade looks like this:

(Source: https://www.ifixit.com/Guide/iMac+27-Inch+2017+Blade+SSD+Replacement/136963)

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Answer 5

padams35

Level 4

3,451 points

Mar 11, 2021 6:37 AM in response to Tony-P

The two parts of a fusion drive do NOT mirror each other.

There is a 32GB SSD NVMe blade and a 1TB SATA HDD. The SSD is essentially used to cache frequently accessed files and maybe buffer writing to disk. Its more of a logical volume spanning two physical drives with smart software for data location management.

A thermal sensor cable isn't required on the newer iMacs.

The 8GB of RAM is not user-replaceable. It is located on the back of the logic board and requires completely disassembling the iMac to access. Its hard enough some Apple Stores and AASP will even refuse upgrade the RAM.

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Answer 6

dialabrain

Level 10

126,755 points

Mar 11, 2021 8:35 AM in response to Tony-P

Tony-P wrote:

Putting the degree of difficulty involved in a RAM upgrade aside for the moment......

I'm just curious about whether the RAM soldered to the logic board or if it's installed in traditional DIMM slots? And is it correct that a max of 32GB can be recognized by this particular iMac?

FWIW, It's not soldered on, it has two slots. There are RAM upgrades available up to 64GB.

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