Home Forums Hardware Mac Desktops & Notebooks NVMe SSD upgrade for 2019 iMac

I have a 2019 27" iMac I purchased from a grey market reseller that has two SSDs installed as a single Fusion Drive, for a total of 3TB (1TB + 2TB). I'd like to replace them with a single 4TB NVMe SSD. The current 1TB NVMe drive is an HP unit (with about 30% life remaining according to DriveDx) and the 2TB is a Samsung QVO 860.

I'd like to remove both drives altogether and I'm leaning toward buying a Crucial brand Gen3 NVMe SSD to put in the iMac's NVMe slot. I'm told using a Gen4 drive wouldn't add any speed as the iMac doesn't have a fast enough bus to take advantage of it, but I wanted to confirm that here. I know there are many brands with 4TB NVMe SSDs out there now, so I'll go with Crucial unless anyone here has a better recommendation.

My main question is about any adapter needed to use the new NVMe drive. I assume there is one already installed for the current HP SSD if it has one at all, since "the 2019 iMac does not have an NVMe slot, it has a proprietary PCIe slot." That quote is from an email from a tech at a local shop I would like to do the work. Is that accurate though? Apple's System Report from this iMac shows the 1TB HP drive installed in the NVMe slot, so I think he might be mistaken.

I will have to pay to have this installation done as I've watched the OWC video about this upgrade and it isn't something I want to try myself.

The tech literally said he does not recommend this and they could not provide any warranty for such an installation. The OWC video didn't show any special adapter to replace the NVMe in the 2019 iMac they used, so I'm asking here for help. Thanks in advance!

According to MacTracker, the iMac (Retina 5K, 27 -inch, 2017) has one 6.0Gbps Serial ata (SATA) slot and one 8.0 GT/s NVMe PCIe x 4 slot. So you should be able to replace the installed HP with another NMVe drive without needing any adapter. Your primary considedration would be heat, not the interface. The internal bus is an Intel Direct Media Interface running at 8 GT/s so that will be the limiting factor as far as drive I/O speed is concerned and there would be no benefit from a faster drive. So you are unlikely to notice any significant performance improvement from this "upgrade". The trick to the conversion is reconfiguring the system as a single drive. There are multiple Knowledge base articles on reconnecting a fusion drive including this one, but the only thing I came up with on splitting a fusion drive is this somewhat dated MacWorld article.

Personally, I want no part of opening up any iMac, and agree that finding an experienced technician is the wisest course, but I would find another shop to do the job, preferably an Apple Certified Repair facility willing to give at least a thirty day warranty on the labor. If you can't find a local shop, OWC can and will do it, if you use their drives. As long as you are at it, be sure you have maxed out the memory in the system. That is where you are most likely to see any performance improvements. You might also consider replacing the SATA drive with a 6 Gbps SATA SSD and using it either as a backup or data volume.

Thanks for the reply. I found a rather long thread at MacRumors detailing upgrades in 27-inch iMacs back to the 2012 model that has a lot of useful info. It includes discussion of the necessary adapters and the best brand of NVMe to use. An adapter is required for the NVMe since Apple uses a proprietary design for theirs.

A couple of notes from your comments. I'm not looking for a speed upgrade so much as a storage space one, though I'd like to avoid any downgrade in the speed. I won't need to reconfigure the Fusion Drive at all since that's one of the things I'm looking to get rid of by pulling out both existing SSDs, before putting in the single 4TB NVMe one. Sorry if that wasn't clear in my initial post. I have multiple external backup drives and have no real need for any additional internal storage, so at this point using a single NVMe drive seems to be the way to go. My only thought was perhaps moving my Music/TV/Podcast libraries to any additional internal storage if I did install it to save space on the boot drive. Perhaps I'll keep the 2TB SATA SSD drive currently installed (it's a Samsung QVO 860) and reformat it as necessary.

I've been warned away from using OWC drives (the "Aura") in any Mac due to reliability issues, including by the tech who answered my email about this upgrade. Unfortunately that tech won't warrantee that work and the only other local Apple Certified Repair place didn't answer my email inquiry about this upgrade. I will try to call that second place directly, perhaps my email just got lost in the shuffle. You're right, it would be best to get at least a 30-day labor warrantee in case they forget to reconnect one of the many internal cables or something.

This iMac already has 64GB of RAM installed, so I'm not inclined max it out to 128GB due to cost and lack of need. I've never gotten close to maxing out RAM usage on this machine and I've edited a fair amount of 4K video.

FWIW, I ditched an external Samsung SSD that was reporting overheating and other early warning NVMe values after less than six months of use in favor of an Aura SSD that has been highly reliable, faster, and significantly cooler (ie. remains essentially at room temperature) for over a year, as do the eight Aura P12 NVMes in my RAID4 array.

Retrospectively thinking about your technician's apparent reluctance, Apple will not warranty any third party upgrade because your iMac has not been tested with your proposed new configuration and even if it works, there is no way of knowing if there may be longer term defects or failures as a result. So, if your tech says she/he cannot guarantee your proposed configuration will work or won't create future problems/failures over time, is reasonable for the same reasons. If the tech says, they think the change will work, but cannot guarantee that it will, but you will still pay for the labor either way, that is at least implied in most private treaty repair agreements unless otherwise specified in writing. So, if the tech seems reluctant to attempt the job, you need another tech, but if she/he is saying "I cannot guarantee this particular configuration will work at all or that it won't cause other long term problems, but it seems doable and I am willing to give it a shot." I would think I had found an honest, and thoughtful technician and the only question is haggling over price.

Thank you for the info about the Aura SSDs, that is good to know. Most of the information I had about them was from many years ago, when SSDs were very new. Perhaps the tech I corresponded with had outdated info as well.

I understand the tech's reluctance to perform the upgrade or at least give a warranty for it. I haven't contacted the other local shop yet but will do that soon. This upgrade isn't pressing. If I can find any tech that is happy to do the work but without a warranty, I think I'll roll the dice and have it done. In the latest post on the MacRumors thread I mentioned in the OP someone used the same Crucial P3 SSD I was looking at for my install and they've had good luck with it so far.

One way I might be able to save money is by putting the NVMe in an external case and installing macOS Ventura on it so it should be easy to boot once placed inside the iMac. The first shop wanted $100 just to install macOS after the uprade, which seems very high to me.

Don't count on being able to boot Ventura from an external drive. Apple is intentionally making that difficult. There is at least one other active thread on FineTunedMac on that subject and the consensus is, you can install Ventura on an external drive, but it will not be bootable. As far as I know, the only way to create a bootable image on an external drive requires the use of Apple Configurator 2 and another Mac, which is likely the explanation for the $100 installation charge. The Genius Bar at your local Apple Store may be willing to install Ventura on the internal drive at no charge once the new drive has been installed.

Interesting. So Ventura could be installed on the NVMe, but even when it was taken out of the external case and put in the iMac it wouldn't be bootable? Or are you simply saying I wouldn't be able to test a proper installation by booting into Ventura on an external drive?

I wonder how all the people doing these NVMe upgrades on the MacRumors thread are doing it. I haven't read the entire thread yet as it's 48 pages long, but I haven't read a single post about anything out of the ordinary to get it to work. No mention of using a second Mac or Apple Configurator 2.

Is that external boot issue a limit of the latest macOS versions or is it based on the T2, Secure Boot and other features in the newer Macs? This 2019 iMac doesn't have a T2 chip in it, the 2020 iMac was the first model to use it.

My apologies for not getting back sooner, I have been distracted by annoying issues relating to beta software on beta versions of Ventura that are apparently unique to Mac Studio computers. But my previous statement obviously calls for some clarification.

Since macOS 12 (Monterey) the boot drive has had three partitions

1. iSCPreboot (500MB)
2. Volume recovery (5GB)
3. Macintosh HD (all the rest)

and each of those partitions has multiple volumes. The installer package creates the Macintosh HD partition, the APFS Snapshot that is the actual bootable image on that partition, and the Volume Recovery partition but it does not create the iCSPreboot volume. The iCSPreboot volume is installed on the boot drive at the factory using Apple Configurator 2. The iCSPreboot is required to initiate loading the rest of the OS. So, if there is an undamaged iCSPreboot volume on the internal boot drive, it is possible to boot the Recovery Drive and from there boot the rest of the OS on another disk drive.

To add further complications, because the bootable image is an APFS snapshot, that can only be created by the installer at install time, the only way to create a bootable clone is using Apple's cloning utility which does not clone the iCSPreboot volume.

Therefore, if the internal drive gets trashed, the only way to get back to a bootable system and the only way to create a stand-alone bootable external drive requires the use of Apple Configurator 2 and a second Apple computer to run it.

By-the-way, as far as anyone can tell, Apple's clone utility is no longer supported and there are no plans for future development.

I've had a lot of trouble following this thread in general, but the underlined portion has me totally confused.

Will you please explain "on another disk drive."

Thanks

Thank you for the very thorough explanation, joemikeb. It now makes sense why the first shop would charge so much to install macOS on a new NVMe drive if it is installed.

Since I plan to own this iMac for several more years I will likely just bite the bullet and pay a local shop to do it if I can find one that will. I haven't taken the time yet to call the second repair shop I found to see if they'll do the work as I'm not in a hurry. If I go through this ordeal and get it to work satisfactorily I will post back in this thread about how it all went.

I really appreciate you taking the time to explain this, I had no idea the Mac boot process had become so complicated in recent years.

The rationale behind the complexity can be summed up in a single word: SECURITY

See this thread for more on the topic of Apple Configurator, and cloning.

Thanks for that explicit but understandable post.
1. I thought you could no longer boot from an external drive?
2. I've got three bootable volumes on my internal drive.
3. I've kept a bootable Catalina clone on my external drive in case of emergency. As far as I know, Catalina is the last version of macOS that could boot a Mac from an external drive.

Sorry for being slow.

1. I thought I had booted my external Catalina while running Ventura, but it was a no-go the other day when I tried, so I guess my memory was faulty (for a change) on that one.
2. This is the info for which you asked. To clarify, HD is my boot volume (13.4.1), CCC1 (13.4) and CCC2 (13.4.1) are internal clones, both of which I successfully booted just the other day, and HD2 is strictly a data volume...music, 3rd part installers, etc.
3. Sword is a clone of the data portion of my boot volume, and HD2s is a clone of HD2, both of which live on a USB drive. (Fun fact: Sword is a shortening of The Sword of a Thousand Truths, an artifact in the excellent South Park episode "Make Love, Not Warcraft.")
4. I'm certain that I was able to boot Catalina while running Monterey.

More: The Catalina I booted is a full clone, not a construct, and I didn't have to go the Recovery route.

Hi, I've still not attempted this upgrade but will need to soon as the fused HP SSD is showing only 24% life left on it according to DriveDx.

In any case, I realized I don't fully understand what is going on with the preboot volume or what it provides. From what I'm reading it's a necessary part of the boot process or at least necessary in order to use Recovery in case there is a problem with normal booting. Can you clarify?

As I mentioned before, the long thread in the forums at MacRumors specifically detailing those who've upgraded their 27" Intel iMacs makes no mention of using Apple Configurator 2 or anything special they had to do after installing NVMe SSDs.

This iMac has an internal 2TB Samsung 860 QVO currently fused with the failing HP NVMe SSD, but you've indicated that even if I installed macOS Ventura on the Samsung and ran the installer from it, it would not create the preboot partition on a newly installed larger NVMe.

Thanks for the help and sorry for being so obtuse.

1. The preboot volume a set of instructions that are hardwired at a specific physical address and contain the instructions needed to load the operating system from the boot drive into memory so they can be used by the processor to boot the system.
2. Intel processors are wired to read the preboot instructions from firmware called the Boot ROM
3. Apple Silicon does not have a Boot ROM, and instead uses a hidden APFS volume, iSCPreboot, located in a hidden 500 MB partition, Disk0s1, which is one of the three partitions on the internal boot drive.
4. Disk0s3 is a 500 GB partition that is created when the OS is updated or upgraded and contains the information necessary to reinstall the previous macOS version.
5. Disk0s2 contains the only APFS volume the user has read/write access to, Data, which nominally contains the remainder of the boot drive's capacity (926.4 GB on a 1 TB boot drive)
6. The macOS installer cannot create the preboot volume as it is used to boot the macOS installer process so that volume must be copied from another Mac using Apple Configurator 2.
7. What the user sees as the system in Finder, Disk Utility, and many GUI apps is a carefully curated virtual construct designed to resemble as nearly as possible the physical structure of the system and drive that was used in macOS 9 and macOS X but has only a casual relationship to the actual physical reality and only exists as a virtual construct contained in the encrypted and sealed Snapshot that is the actual bootable entity and is created by the macOS installer.

I do not know the specifics as related to Intel Macs, but given the current versions of macOS are targeted for Apple Silicon, I believe it is safe to say what is running on Intel Macs adds another layer of virtualization.

Your Fusion drive is another issue altogether. When I replaced the HD is a fusion drive, I first had to separate the HD and SSD into separate volumes, the I elected to use them as separate drives, but that was long before macOS 10. These Apple instructions will explain how to rejoin the pair into a single fusion drive.

Ok, thank you for trying to explain. It's still very unclear to me so maybe I'm just stupid.

Since no one on that MacRumors thread has appeared to have any trouble installing macOS after replacing the internal NVMe SSDs (and there is no mention of using Apple Configurator 2 to do so), I'll trust any local Mac tech I can find will know how to do it properly. The thread details user experiences after installing these upgrades on 27" iMac models from 2012-2019.

As a side note, currently the drives on my iMac show as two separate volumes now after I had to wipe and reinstall macOS about two years ago, as boot times were getting very slow (taking about 20 minutes). However, it seems to be just a cosmetic issue and the drives are still fused, so I didn't bother to try to fix that. Once the new internal 4TB NVMe is installed as the boot volume and the existing internal Samsung 860 is a separate volume, I will no longer be using fused drives in this iMac.

I will be wiping all the data from both drives before taking it in for that upgrade after making backups with both Time Machine and Carbon Copy Cloner.

You aren't stupid, just understandably confused because you are dealing with lots of computer technology in flux as it is evolving. The fusion drive was an interim solution when SSDs were new and expensive and are no longer supported in current versions of macOS. The APFS file system is designed specifically for use with SSDs although it will work on HDs and recent versions of macOS will only run on volumes formatted APFS. The situation is further confused by Apple's attempt to make the new system appear to the user as if it were the old, familiar HD oriented HFS+ file system. And all of this running on Intel processors that macOS supports through yet another virtualization layer. If this feels as if you are seeing your computer through multiple layers of smoke and mirrors, you are getting an accurate view of the new virtual reality.

When you reinstall the OS remember your new 4TB SSD will be attached to a significantly slower port than the SSD that was part of the fusion drive. So, for optimum performance, you may want to install the OS on the old SSD.

The new 4TB NVMe SSD will be put in the same port the old NVMe SSD was. I'm simply taking out the 1TB HP NVMe and putting in a faster 4TB one. It will no longer be fused with the 2TB Samsung QVO currently in the SATA slot, so I guess that could make it slower than fusing them, I don't know.

From what I could find online, the PCIe x4 NVMe port is substantially faster than the 6.0 Gbps SATA port. The new 4TB NVMe SSD is also faster than the 1TB HP it will be replacing.

That is the ideal configuration and what I meant to imply, but obviously did not. Fusing the drives is NOT recommended -- as I said, macOS no longer supports Fusion drives.

The new 4TB drive may be faster, but the NVMe port it is plugged into will not be any faster and will limit the throughput from the drive, so don't expect it to be any faster than the 1TB NVMe you are replacing.

Never, in more than 20 years of MFIF and FTM, has a thread ever been so incomprehensible...gone so far over my head!

Yes, this one was a stretch for me too, and my career was in IT as a consultant as well as being a longtime hobby.

I guess we have hackers and security issues along with our computers being open to the world via the Internet to thank for Apple having to take such drastic measures to keep our data safe. Oh well.