An External SSD Gave My iMac a New Lease on Life

Originally published at: An External SSD Gave My iMac a New Lease on Life - TidBITS

Prices for SSDs and Thunderbolt 3 enclosures have plummeted, so Glenn Fleishman finally bit the bullet to upgrade the storage for his lagging 2017 iMac. Doing so probably extended the useful lifespan of his iMac by years.


Amen Brother! Except for the brand of external SSD, my story is very similar. When I updated to Catalina my 2017 21.5-inch iMac started to feel like it was slogging through thick mud. Finder copies of even the smallest files seemed to take forever. I finally bit the bullet and attached a 1 TB SSD to a Thunderbolt 3 port, and it really WAS like acquiring a brand new iMac. Since that time, I have been counseling the members of my user group to avoid updating past High Sierra or Mojave if they still need to keep running on spinning rust.


-10 points for using the term “spinning rust”


When I tried to upgrade my iMac18,3 to Catalina, the installer refused, it said I had a SMART error on my Fusion drive. Well jeez I’m glad I found out before it failed, I had no idea. I backed up the Fusion drive successfully and cut open my iMac, I installed a 2TB OWC Aura Pro X2 internal SSD, wow it’s fast. I also put in a 4TB hard drive for backup, then I realized I probably want an external drive for backup oops. Oh well, you can’t have too much storage now.

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I did exactly the same thing to my 2017 27" iMac. I debated about swapping out the internal Fusion drive, but opted instead to use the OWC Envoy Express with a 1 TB drive. The difference was dramatic, and Big Sur now launches in half the time it did, as does Photoshop. In over 6 months I haven’t had a hiccup and continue to use the Fusion drive (1 TB) as storage for my Plex recordings. This is a highly recommended upgrade and one I’d recommend to anyone looking for better performance over the standard Fusion drive in an iMac!

good info. I never considered using an external boot drive for anything other than testing / emergencies.

fusion drive sounded good but turned out to be a dud in implentation. It’s gotta be SSD.

I did open up one of the slim imacs that have screen glued to aluminum frame. I was a bit surprised I was able to get it done without breaking glass.

Not something I’d like to do again.

External option sounds much better.

Would you recommend on a Mac that only has Thunderbolt 2?

I just purchased a 2 TB SanDisk Extreme Pro to use as my Carbon Copy Clone for my iMac 27" 2019 (1 TB SSD). So did the CCC on it, using Thunderbolt 3 connection. Fast cloning for the first clone! Then I ran Disk Utility (as I always do) on the new external SSD. As always, DU tells me that my Data Disk could not be examined and I need to back up and reformat. This is a constant headache for me with Catalina!!

But I went ahead and rebooted the iMac using the external SansDisk as my boot disk. Booted up beautifully! Very fast. Everything there. Had to enter in some passwords and sign in to Dropbox, etc. But it worked flawlessly.

Now if I can only stop the stupid OS on the computer from constantly telling me external backup and clone drives are corrupted and need to be reformatted. A regular event for me. Thank heavens I have backups of backups!

Glad to hear of the new computer life for so many of you using external SSDs.

There’s nothing inherently wrong with hard drives, but it’s important to know their limits. They’re not nearly as fast as SSDs and as such are not appropriate for certain applications:

  • The system/startup volume when running a modern OS
  • Scratch/workspace/project storage for high bandwidth projects like video editing

On the other hand, they work just fine for mass storage, where performance is not critical, including:

  • Backups
  • Storing documents for office apps
  • Media collections, including video, especially when the primary usage will be playback, not editing.

Given the price difference, a hybrid system where the OS, apps and certain kinds of documents are stored on an SSD while the rest is on a hard drive, makes perfect sense to me.

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The speed is great, Glenn. I want to do the same thing, but what about reliability? I’ve read dozens of reviews for many different enclosure for NVMe SSD cards, and there seem to be very serious issues with overheating.

Do you have any worries about that?

I’m not totally sanguine about it, but I picked a more rugged enclosure from Other World than I might have if it were a drive I used for less than primary purposes. I could probably get a little USB fan to blow air on it in the summer! So far, the outer skin feels mild.

That’s compared to an Envoy Express, which I got for backups and testing, and after running a full clone backup to it, whew, the case was almost untouchably hot.

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I was too worried about something going expensively wrong in opening the case up, and figured the benefits just weren’t worth it. I should also note that with OWC offering a Thunderbolt hub, that changes things, too. The iMac I have doesn’t have enough Thunderbolt 3 ports for my liking. I have 100% full now! But I can get the OWC hub, which works with Big Sur, and add a net of two Thunderbolt 3 ports. (It has four ports, but one is a host port and one replaces the port it fills. There’s also a USB 3.2 port.)

They’re not cheap, but they would give me flexibility. I would keep my external SSD plugged directly into an iMac port, but the external monitor and other Thunderbolt 3 uses could be relayed through the hub.


If you can find a Thunderbolt 2 enclosure for an SSD, it’s probably SATA III inside, so you might just want a USB 3.0/3.1 Gen 1 style enclosure, since it will be cheaper. Unless you’re short of ports. Per the article, you could see a five- to 10fold average improvement in disk access with a SATA III-packaged SSD, so not terrible at all!

Last Black Friday I got (all for best prices) an Envoy Express T3 enclosure, a 1 TB 970 EVO SSD, and 64GB of Crucial RAM for my base 27” 2019 iMac with a Fusion drive. I also added a 2TB Seagate Barracuda 3.5 HD in an enclosure for a surprising low cost for a pleasingly fast and quiet backup drive.

The external 970 EVO has Big Sur on it and has been only lightly used so far. I ran every speed test and it performs as good as expected in the Envoy Express enclosure. Note the controller in this enclosure does not give the Thunderbolt 3 speeds of enclosures in the $150 and more price range. I assume I benefit “heat” wise by not being able to use the 970 EVO at full speed. I keep a cheapo thermometer on top of the enclosure and touch the drive all the time and it’s only ever warm at 90-95 degrees Fahrenheit. It has never been hot or deviated even for heavy writing. The only thing maybe not perfect is since the Envoy Express enclosure is bus powered, it’s short cable limits where I can place it. Small price to pay.

The speed of the 2019 iMac running on its Fusion drive with Catalina seems similar so far to running Big Sur on the external SSD in said configuration.

Ah, that’s interesting, especially the temperature comparison with the Envoy Express. Apparently the choice of chipset makes a huge difference. I’ve read that the Realtek 9210 is vastly better for heat than the JMicron or ASMedia chips. I wonder if the more premium OWC enclosure uses that new chipset.


Anybody know if iMac firmware gets updated when you install an updated macos on an external? On an MBP at least…it only gets updated with an original Apple SSD installed and not with an OWC one instead.

My experience with running my 2014 iMac from an external USB 3 SSD was that it was entirely usable, but definitely not as fast as the internal SSD (which failed in my case). If you’re comparing against a Fusion Drive or hard drive, however, it’s definitely better.

I actually did cut open a pair of 27-inch iMacs to replace the internal SSDs. It’s not for the faint of heart, but it is doable and just takes a lot of time and care. And the right tools and repair parts.

That’s fascinating, @glennf. I did not have that option with my late-2012 27 inch iMac, which is currently on the bottom of the “supported” list for OS upgrades. It does have original Thunderbolt, but I think that would be a bottleneck for an external ssd.

But I did slice it open about 4 years ago, and replaced the 1 TB hard drive (which at the time I purchased was a definite splurge) and replaced it with a 1TB SSD. Same major surge in performance, and even though I had to replace that machine for production work last summer because of a heavy video editing demand, it’s still quite able to keep up with secondary tasks, videoconferencing, and being used via screen sharing to run legacy Adobe apps.

I am hoping for a useful 10 year run for that iMac.

Definitely compared to using an internally replaced drive, as I think you can get PCIe speeds internally.

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I’m not aware of this problem for any Mac. Usually the firmware update runs after install and restarts the Mac a couple of times. Do you have a pointer to something that explains the problem you had?

Agreed on that. But my limit is now iPhones 7 and up. I officially destroyed my home button last November while trying to replace the battery. [edit] It was a good excuse to jump to an iPhone 11, which apparently is equipped with an infinite power source.

Compared to an iPhone, my iMac looked like a pre-1980s car under the hood.