I love Retina iMacs. So much so that I took a chance and bought a used 2015 low-end Core i5 iMac with a 1TB Fusion Drive (which combines a 24GB NVMe SSD and a 1TB hard drive)—a machine that’s actually slower than my 2012 Core i7 iMac. I bought it with upgrading in mind, which is where the fickle finger of fate came into play.
I wanted to upgrade the iMac’s NVMe SSD with something that offered more space but was relatively less expensive (in other words, not sold by Apple). I found conflicting info about the upgrade, though. Authoritatively stated advice such as “You’ll kill the machine and possibly yourself” was hardly useful (not to mention, completely incorrect), while “Well, it worked in my 2017 [iMac]” provided hope, but no specifics.
After buying the iMac (it was a bargain I had to jump on) and later talking with vendors, it became apparent that my leap of faith (and general storage knowledge) had been justified.
A disclaimer: if you bought a 21-inch iMac with a standard hard drive, you’re out of luck—these iMacs didn’t have an PCIe SSD slot on the board. But there is a viable option you can read about—NVMe via Thunderbolt. If your iMac shipped with a Fusion Drive or SSD, read on.
Another disclaimer: if your iMac is still under warranty, this will void it. You also run the risk of permanently damaging your iMac. If you’re careful, you shouldn’t, but stuff happens.
With the disclaimers out of the way, here’s how you can upgrade an iMac’s NVMe SSD with something cheaper, faster, and more capacious.
Finding a NVMe SSD for the upgrade
As I intimated, there was never any question that the NVMe SSD could be upgraded, just whether it could be done for a reasonable price. A huge issue is that Apple uses proprietary connectors. OWC’s compatible drives on Newegg were 40 cents per gigabyte, and Apple’s on Amazon were an incredible $1 a gigabyte! This is 2019: standard M.2 2280 NVMe SSDs start at 15 cents per gigabyte!
Perusing further, I found Apple-compatible SSDs for around 30 cents per gigabyte. That’s better, but they were from unfamiliar companies I was unable to chat with. Finally, I stumbled on a company with an office in Birmingham, Alabama called Fledging, whose Feather drives run around 25 cents per gigabyte and are available in up to 2TB of capacity. The company armed me with a number of relevant tips, and sent me a 512GB M13 Feather SSD kit with macOS High Sierra pre-installed.
While 25 cents per gigabyte isn’t bad—the Feather drive turned out to be a good all-around performer—I was enamored with the idea of using a less expensive M.2 2280 drive. I already had a bunch and they’re not all cheapos.
I settled on the Western Digital SN750 Black for the experiment, but you could easily make do with something such as Crucial’s P1. Also, you need a sub-$20 adapter from Sinetech to use a M.2 2280 SSD in an iMac.
The Sinetech adapter is actually made for MacBooks, and there is a subtle difference in the distances between MacBook and iMac mount points. The end result is that the adapter is just a hair too long, and the drive just a shade more so. It can still be installed, but it’s not a perfect fit. Then again, it’s inside the iMac where you’ll never see it. Out of sight...
It’s been reported that one of the most popular and fastest mid-range NVMe SSDs, the Samsung 970 EVO Plus, currently won’t play nice with Macs. I had intended to test the 970 EVO Plus as an upgrade, but while formatting it in an external PCIe enclosure, it crashed my other Mac. I took the hint.
Installation of the NVMe SSD
As I said before, this will void your iMac's warranty. You also run the risk of permanently damaging your iMac.
What’s nice about the Fledging NVMe is that it’s a plug-and-play device. If you don’t opt for a plug-and-play NVMe, you need to create an installation USB thumb drive with a full copy of macOS High Sierra or later. There’s no support for third-party NVMe drives in macOS verions prior to High Sierra. You need the installation drive because when you replace the main drive in an Mac, you lose the ability to restore from the internet until you’ve reinstalled macOS.
I opted for High Sierra because I know it works fine with Boot Camp. Mojave’s issues with Boot Camp may be over, but I opted for tried and true.
Another thing you might consider is upgrading the hard drive to a 2.5-inch SSD. I did.
I won’t bore you with the complete tear-down instructions for a 2015 iMac. Frankly, I can’t do better than the easy-to-follow and granular guide on ifixit.com, which is what I used the first time. The procedure is hardly difficult, but it requires patience, a modicum of finesse, and some tools.
One thing I will say is to be careful removing the display and handle it with care. iFixit sells a great roller (see above) for spudging the display off that eases the job considerably. Use a large workspace, and remove move anything hard or pointed that you could conceivably bang into and break the glass. Pad below the iMac and prop it so it’s tilted back.
After that, the whole deal consists of delicately unplugging a few cables, undoing quite a few Torx screws (you’ll obviously need torx drivers), then removing the speakers, power supply (don’t touch the bare solder joints on the back), and logic board. You’ll find the NVMe SSD on the back of the latter, secured by one screw. It’s simple, but a few pain points:
A post for the power supply is also a screw securing the motherboard.
There’s a captive screw behind the motherboard that you access through a hole in said board.
The webcam and primary display cables have flip-up locks, don’t just yank on them.
Both large cables connecting the power supply with the motherboard have latches. You must press these to enable removal and the large cable requires a fair amount of force. Don’t just yank.
There are upward-facing screws behind the fan that are easy to forget. These are also slightly different from the others with a raised secondary flange beneath the actual screw head.
Remember how I brought up the fit issue with the Sinetech adapter? I was able to screw the assembly in place by tilting the screw with its tip just in the hole, then pressing it towards the assembly. This did unfortunately induce a bit of a bow in the SSD, but shouldn’t be a problem. If you’re brave, you can deepen the adapter’s and SSD’s indentations a bit with a round file and much care.
Once you have the drive installed and are ready to test it, I recommend that you only do the bare minimum of reassembly (minimal screws, leave the display untaped, no speakers, etc.) so that you don’t have to repeat the entire disassembly again should the something be amiss with the drive or the procedure otherwise doesn’t work.
When the computer is operational again, boot with the USB disk you created, run the High Sierra Disk Utility to partition the drive and you should be on your way. Then complete the reassembly process.
Which computers, which drives
There is no PCIe SSD slot in 21.5-inch iMacs that didn’t ship with Fusion Drives or SSDs. And though 2012 iMacs (anything with a Fusion Drive and any 27-inch model) had M.2 connectors, they SATA only, which means you'll get the same speed boost by upgrading the hard drive to an SSD--a much easier process.
In 2013, the PCIe bus was deployed, and though these SSDs were AHCI types, most of the computers are said to support NVMe. However, it's only PCIe 2.0, so even a low-performance NVMe SSD will do, as you’re limited to 900MBps (2 lanes)/1.5GBps (4 lanes) throughput anyway.
With the late 2015 iMac, the PCIe implementation revved to 3.0 which can leverage the performace of even the fastest drives available, such as the WD SN750 Black that I chose.
As to performance. Much of NVMe’s kick comes from the insanely quick (10X SATA) seek times offered by every drive I’ve tested except one, which was still three times faster than SATA. The greater throughput offered by the more expensive drives only comes into play with large, multiple gigabyte transfers.
If you regularly work with large video files or write large amounts of data, you want the pricier types. Also, stay away from lesser capacities (256GB or smaller) which often have fewer chips and slower writes. Avoid QLC (Quad Level Cell/4-bit) drives and cheaper TLC drives where throughput drops drastically once they run out of cache. Check out PCWorld’s SSD reviews for info on individual models.
If you do switch out the hard drive during your upgrade, and find your fans spinning at full speed, there’s a simple fix from CrystalIdea called Macs Fan Control which allows you to tweak all of a Mac’s fan settings, obviating the need for an expensive cable.
I wanted faster and I got it. Big time. Directly below are the numbers for the original 24GB SSD. Not bad, but not bleeding edge by any standard.
Next up is the easy, affordable plug-and-play upgrade Fledging Feather M13 SSD. It’s convenient as well, coming with High Sierra pre-installed, though for $5 you can have a USB stick that allows you to install Mojave.
Note that the write performance numbers the company sent me were quite a bit higher than this, but they were garnered using a 2015 i7 MacBook Pro. The CPU does make a difference.
As you can see, the Feather M13 is a fantastic reader. But it varied from a good (1.2GBps) to mediocre (600MBps) writer, depending on whether the cache was full or not. Regardless, the 2.8GBps reads and lightning seeks mean you still get that NVMe kick in the pants, and of course, you don’t have to worry about a slightly ill-fitting adapter.
Just in case you aren’t so sanguine about opening up your iMac, here’s the alternative I talked about—NVMe via Thunderbolt. Below are the results from the same 2015 i5 iMac, with an Akitio Thunder2 PCIe enclosure housing a Samsung 970 EVO SSD. The older 970 EVO works just fine (I’ve run High Sierra from it for over a year), where the 970 EVO Plus did not.
Though NVMe over Thunderbolt is not always quite as smooth an experience as an internal NVMe SSD (there seems to be the occasional slight pause), it’s still faster, and though not cheap, a good alternative if you’re shy about opening your system.
Last, but not least, is the Sinetech adapter paired with a 1TB WD Black SN750 NVMe. This is what I had in mind—nice, consistently large numbers across the board.
Don’t listen to the doom-and-gloomers in the forums, you most decidedly can upgrade the NVMe SSD in your iMac to something faster and more capacious without forking over your life’s savings. I tested the 2015, but I’ve seen 2017 models upgraded, and Fledging assured me any Mac with an SSD connector can be upgraded.
Given the price, quality and speed of the plug-and-play Fledging Feather, that’s likely the best option for the average user. On the other hand, I’m pretty darn happy with the WD Black SN750 and the adapter, despite the slightly ill fit.
Either way, it’s an upgrade that will make you smile. And not in small part because you survived taking your Mac apart.
This article was edited on 12/14/19 to clarify the discussion on which models have which technologies on board.