Replace Fusion Drive in 27" iMac

Opening an Apple Computer, especially an iMac, will require special tools to get it open

It will also require some very special knowledge, by the user, to properly disconnect various cables within the computer

All this, before one gets to removing and replacing the SSD drive of this Fusion Drive

An alternative to extend the life of this machine

From another User Tip on running the computer entirely from an External SSD Drive

No opening of computer required

Use an external SSD as your startup disk … - Apple Community

peterpatter wrote:

Will the new external SSD (connected to the 27" iMac via a USB-A cable with an adapter) be replacing the existing Apple SSD Controller of 28GB capacity? This is indicated as an APPLE SSD SM00321.

It would be replacing the entire Fusion Drive.

If the SSD in your Fusion Drive is showing up as having only 28 GB of capacity (total), that would indicate that you have one of the 1 TB Fusion Drives that Apple shipped starting in Late 2015. (The original 1 TB Fusion Drives came with a much more reasonable 128 GB of SSD storage.)

Your 1 TB Fusion Drive has (1.028 TB) of storage – 1 TB on a mechanical hard drive, 0.028 TB on a SSD.

I am planning to purchase an SSD (LaCie) to be my new startup drive. Which would be better, a 1TB or a 2TB SSD? Is larger better, or is smaller OK? I need some education as to what it actually does.

Depends on how much you need to store on it. You should probably leave 10% – 15% of the space on a SSD free, so if you have 100 GB or more of space free on your current Fusion Drive, a 1 TB SSD might do. If you were close to filling the Fusion Drive, a 2 TB SSD might be in order.

There are three rough categories of SSDs you can use with a 2017 iMac.

• USB 3.0 / SATA SSDs – Slowest, cheapest
• USB-C (USB 3.1 Gen 2) / NVMe SSDs – A bit faster, and these days, not much more expensive than SATA ones. You would need to plug these into one of your USB-C / Thunderbolt ports to get the USB 3.1 Gen 2 speed.
• Thunderbolt 3 / NMVe SSDs – Fastest, but significantly more expensive than the others.

peterpatter wrote:

Hi PRP_53.

Sorry I've been so long in responding to your most welcome suggestions. If I operate my 2017 27" Fusion Drive iMac from an external SSD, am I then, in fact, using only the excellent screen, with everything else operating from the external SSD?

An external SSD does not replace the CPU or GPU in your computer. It is just storage.

You'd still be using all of the parts of your Mac except the Fusion Drive. (It would now be just a "second drive", and if you had no reason to believe it was actually failing, you could use it an extra backup, or for extra storage.)

Also, would my Apple Extreme Base Station and printer, scanner etc. still connect to the computer via wifi, or would they have to change over to the new SSD? Any comments would be welcome.

Those things connect to your computer, not to your SSD.

Unless you changed the software that you are running on your computer – the operating system and/or drivers – they would not be affected at all.

peterpatter wrote:

. Would the external SSD appear in Finder and as a Desktop Icon, in addition to my LaCie backup drive, which is used for Time Machine?

yes, as long as you have the Mac set to recognize external drives in the finder selections for sidebar and desktop.

peterpatter wrote:

Hi Servant of Cats,

It's me again. At my local Apple Store, the LaCie rugged 2TB SSD is indicated as being suitable for an iMac (Retina 5K, 27-inch, 2019–2020). As my iMac is a 2017 model, is it OK to go ahead with the purchase? The 2TB model costs quite a bit more than the 1TB SSD.

Many thanks,

peterpatter.

I'd pass on the Apple Store's LaCie Rugged Mini SSD ($180 for 1 TB, $300 for 2 TB).

• I don't think there's a huge advantage in paying extra for a 'rugged" dust and water resistant enclosure for a SSD that will spend its life attached to a desktop Mac.
• The "USB 3.2 Gen 2x2 technology" mentioned in the product description won't do you any good. Your Mac doesn't support USB 3.2 Gen 2x2 – so the connection would fall back to at most USB 3.1 Gen 2 speed. Why pay for speed you can't possibly get?
• The exclusion of your iMac from the extensive Compatibility list is troubling.

A better high-end alternative would be something like this Thunderbolt 3 SSD:

• Other World Computing – Envoy Pro FX ($280 for 1 TB, $330 for 2 TB).

That one can run as a Thunderbolt 3 SSD when connected to a Thunderbolt 3 port – and fall back to USB speeds when connected to USB-only ports.

In my mind, a 2 TB Envoy Pro FX would be a much better choice than a 2 TB LaCie Rugged Mini SSD – given what we know of connection speeds, and of the omission of your iMac from the LaCie compatibility list.

However, even an Envoy Pro FX would likely be overkill. If you are willing to go for a nice mid-range SSD, I believe you can get something that would, overall, be a satisfactory upgrade from your Fusion Drive for much less money. Some alternatives that you might want to consider:

• Crucial X9 Pro Portable SSD for Mac ($95 for 1 TB, $150 for 2 TB at current B&H Photo Video prices). Since you would be using this for a startup drive, I would recommend getting a "for Mac" version. (A recent thread claimed that to use one of the non-Mac ones as a Mac startup drive, you might need to first update firmware, using a tool that runs only on Windows.)
• Other World Computing – Envoy ($120 for 1 TB, $200 for 2 TB).

Assuming that you're in the market for a 2 TB SSD, that's $100 - $150 more in your pocket than you would have if you bought a LaCie Rugged Mini SSD that – on your iMac – might not run any faster.

The advise from @ Servant of Cats should be followed

Yes, if you have Finder > Settings… set up right.

There are two tabs of interest there. The General tab controls whether icons show up on the Desktop, and the Sidebar tab controls whether entries show up in the sidebars of Finder windows.

"Hard disks" is a bit of a misnomer. No Macs shipping today come with internal hard disks; they all come with internal SSDs. But Apple continues to use the name "Macintosh HD" and the label "Hard disks".

Re: “my 2017 iMac only has USB-A ports and an ethernet port on the back. Can I get an adaptor so one of these ports can become a USB-C / Thunderbolt port, to get the USB 3.1 Gen 2 speed?”

There is no adapter that you can get to turn a USB-A port into a much faster and more capable Thunderbolt port. You can get USB-A (USB) to USB-C (USB) adapters, but your USB-A ports only support USB 3.0 speed. An adapter could not raise that speed.

If your Mac is indeed a 2017 iMac, then it has two USB-C / Thunderbolt ports.

iMac (Retina 5K, 27-inch, 2017) - Technical Specifications - Apple Support

https://cdsassets.apple.com/live/6GJYWVAV/start/ma1789_imac-5k-mid2017-qsg.pdf

peterpatter wrote:

Hi Servant of Cats.

You mentioned above: with an external SSD I'd still be using all of the parts of my Mac except the Fusion Drive. (It would now be just a "second drive", and if you had no reason to believe it was actually failing, you could use it an extra backup, or for extra storage.)

To use the old Fusion Drive as a second drive for storage, how would I get it to appear in the Sidebar and Desktop, so I could drag and drop Folders into it?

It would continue to show up as "Macintosh HD".

However,

• The icon in the upper-right-hand corner of the screen would be the one for the current startup volume. E.g., if you named the external SSD "Macintosh SSD", you would see the icon for "Macintosh SSD" in the corner, and the icon for "Macintosh HD" would be below it.
• Many of the standard "Favorites" in Finder sidebars are relative to the startup drive, or to your user directory on the startup drive. So when you were started up from the external SSD, they would refer to places on it.

peterpatter wrote:

Hi Servant of Cats,

Apologies for having taken so long to respond to you. I've been thinking too much about my situation. I still need advice, and more knowledge, before proceeding with the external SSD.

Will the new external SSD (connected to the 27" iMac via a USB-A cable with an adapter) be replacing the existing Apple SSD Controller of 28GB capacity? This is indicated as an APPLE SSD SM00321.

I am planning to purchase an SSD (LaCie) to be my new startup drive. Which would be better, a 1TB or a 2TB SSD? Is larger better, or is smaller OK? I need some education as to what it actually does.

Many thanks for all your previous comments and suggestions,

peterpatter.

How deep is your pocket book ?

How much can you afford to pay ?

When the External SSD Drive is used as you Startup Drive

Both the small 28 GB Internal SSD drive and the Rotational / Spinner drive are not longer used at all

All functions of the Operating System are performed from and on the External SSD Drive

I had a late 2013 iMac with the 1TB fusion drive that I replaced last year. I think you do need special tools to open it up. You might even have to cut open the back. Also, I agree that you can't just use a USB-A to USB-C adapter to increase transfer speeds.

I noticed that you're running Ventura 13.7.1 (operating system). Can your computer OS be updated any further?

My 2013 iMac actually ran well (Catalina) up until the summer of 2024. But I was living in fear due to lack of updates.

peterpatter wrote:

Thanks so much for your information. As I've never, so far, had need for the USB3 ports, I had forgotten that they were there. How stupid can I be? To transfer files between my iMac and my MB Air (M1 chip), is a cable between the respective USB3 ports the best way of doing this?

If you are talking about Target Disk Mode or the equivalent, I do not believe that a USB cable would let you use the iMac as a Target Disk for the M1 MacBook Air.

Transfer files between two Mac computers using target disk mode - Apple Support

"Note: If either of the computers has macOS 11 or later installed, you must connect the two computers using a Thunderbolt cable."

You would need to use a Thunderbolt cable to connect the two Macs. The Thunderbolt cable would have USB-C plugs on either end, but would rated to carry Thunderbolt traffic (and would be more expensive because of that).

If you wanted to use the M1 MacBook Air as an "external drive" for the 2017 iMac, then you could use a USB cable that went from USB-A or USB-C (on the 2017 iMac end) to USB-C (on the M1 MacBook Air).

Transfer files between a Mac with Apple silicon and another Mac - Apple Support

I'm guessing it's easier to bypass this, and do the transfer with the aid of

• An external drive (plugged into one Mac at a time), or
• iCloud Drive (for small numbers of files) – put files into iCloud Drive and they will be available to either Mac

If you were setting up a new Mac for the first time, and wanted to transfer things from the old Mac, a common way to do that is to take a current backup (Time Machine, Carbon Copy Cloner, Super Duper!) from the old machine, attach it to the new one, and tell Migration Assistant to migrate from that backup. But it sounds like you already have both machines set up and so would not want to do a blanket migration.