External SSD-drive on thunderbolt port iMac makes iMac MUCH faster???

You will want complete and current backups, whether Time Machine or otherwise. This as your data is the most important part of this configuration, and slowdowns can be associated with corruptions and with hardware problems.

• Back up your Mac with Time Machine - Apple Support

Some hardware-related background, first.

Some background on performance, though a correctly-functioning Fusion will sprint better than the HDD discussed in the following:

• Why is my hard disk drive iMac so slow? - Apple Community

How to use an external storage device to boot:

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

This’ll probably involve an external USB 3.x storage device, not Thunderbolt. Your iMac does have Thunderbolt and it is faster than USB 3.x, but spending on Thunderbolt storage hardware here seems less appropriate than spending on a newer iMac or Mac mini.

But….

Whether a USB 3.x SSD helps here is not clear, as this could be a Fusion problem, or insufficient physical memory, or something else such as add-on apps. And I wouldn’t expect a big performance boost over a correctly-working Fusion, in what might be an iMac with a minimal memory configuration.

What to do? Well, let’s see the configuration…

As for other potential causes of degraded performance, some add-on apps can get involved, and insufficient hardware resources as mentioned too. Here, please download and run EtreCheck (the free version, don’t need the paid version here), and share the results to the clipboard. Then open a new reply here, and press the Additional Text button (the button that looks like a printed page), and paste and post the hardware and software configuration report here. From that, we can get a little more detail about what is installed and what is running here.

Then (depending on what the report shows) maybe a check of the storage diagnostic data.

As for Artificial Inanity…

AI is the canonical example of “trust, but verify”. Or all too often don’t trust, and do verify. All sorts of sycophancy and other sorts of “fun” can be awaiting there.

nldre wrote:

i've a 2019 21,5" iMac with 1Tb Fusion Drive. It's getting slower en slower last years and while editing photo's become unworkable.

Apple's 1 TB Fusion Drives originally included 128 GB of flash (SSD) storage. But Apple got stingy in Late 2015 – and slashed the amount of SSD storage.

Your 21.5" 2019 iMac's Fusion Drive combines

• A slow 2.5", 5400 rpm 1 TB hard drive, with
• 32 GB of flash (SSD) storage

That 32 GB of flash storage is "prime real estate", but there is not nearly enough of it.

It is quite likely that a USB-C (USB 3.1 Gen 2) SSD would provide much better performance than your Fusion Drive, and a Thunderbolt 3 SSD definitely would. That is, if your internal drive is not failing. (If the internal drive is failing, you might be able to bypass that by simply adding an external drive – or you might not. A failing drive could throw errors that cause the Mac to crash even when started up off an external drive.)

AI says I should bij for example a Samsung T7 external SSD and connect it to my thunderbolt port and installing MacOS on that drive. than the Mac starts within 30 seconds again and programs like photo and iMovie are much quicker.

I went to 3 shops today but they all advised NOT to do so. On the internet are a lot of success stories.....

Some considerations:

• SSD prices have gone through the roof. For instance, you mentioned the Samsung T7 external SSD. On one of the sites I checked, a 1 TB version cost $230. a 2 TB version cost $430, and a 4 TB version cost $1000. A few years ago, I purchased a similar Crucial 4 TB SSD (now discontinued), and I'm pretty sure it was under $250.
• Sequoia (the latest version of macOS your iMac can run) will fall out of the "most recent three" in about a year from now, when macOS 28 comes out. How dependent are you on vendors who support only the most recent three?

nldre wrote:

I went to 3 shops today but they all advised NOT to do so. On the internet are a lot of success stories.....

I don't know why a repair facility would suggest to NOT try that. maybe they wanted to upsell you on having the Fusion Drive internally upgraded to an SSD? but the success stories you've seen are factual. using an external SSD as a boot drive is the easiest way to speed up a Mac that has a Fusion Drive, or straight HDD Mac.

Has anyone done this already and what is your experience

I use two external SSDs. but not for performance issues. my iMac is 100% SSD configured. but I use one external SSD to run Catalina when I need to use a piece of antiquated hardware, as well as one that I use to run linux. they both perform well, and are pretty quick. and, funny enough, they are both Samsung T7 drives.

If you have an Intel iMac you can connect your external SSD to your Mac and clone the contents of the Fusion Drive to your EHD according to this user tip: Using Carbon Copy Cloner to Make a Bootable Clone of Intel Mac.

It's just another option to move forward.

in your report, I didn't see any of the usual suspects that negatively affect performance. but you do have the Fusion Drive that uses the VERY TINY 28GB SSD. to me, that says it all. I think that is where your issues are coming from.

If all else fails and it's a long shot you might try uninstalling Zoom. I had a Mac Mini M4 with Zoom installed and I was having problems. I uninstalled it and all of its support files and my problem went away. I have no idea if it will help you but as I said: if all else fails. It can always be reinstalled.

It would appear Time Machine is running, but without access to its archival storage. Is this correct?

You are low on free storage space, but you do have a fair amount of storage available; storage that can be freed up. (Again, likely local snapshot backups, because Time Machine can’t get at its archival storage.)

I’d likely remove OneDrive as that can sometimes get chatty.

I’d also either connect the archival storage, or would shut off Time Machine.

Performance is pretty good, but I’d expect a combination of little physical memory and little free storage space is helping, possibly with chatter from OneDrive.

Rather than limiting this to an M4, I’d also consider an M2 or M3, any of which will be a big step up from an iMac i5 8 GB Fusion. I’d skip the iMac M1, though.

You had enough RAM for what you were doing at the time that you generated the EtreCheck report.

Virtual Memory Information:

Physical RAM: 8 GB

Free RAM: 33 MB

Used RAM: 5.93 GB

Cached files: 2.03 GB

Available RAM: 2.07 GB

Swap Used: 59 MB

macOS put most of the RAM that wasn't immediately needed to work holding "Cached files" (2.03 GB), leaving only a bit of RAM (about 0.04 GB) completely idle. That was an optimization; if the Mac needed the data again, before it needed the RAM, it could have saved a slow trip to the Fusion Drive to get it. If it needed RAM first, it would have simply dumped some of the cached data to make the RAM available.

Swap Used is fairly low at 59 MB (lower is better). And I bet if Activity Monitor had been running, it would have shown all Green on the Memory Pressure graph.

It's possible that if you are running heavy workloads at other times, 8 GB might not be enough RAM – but that would be something to determine by running Activity Monitor at the same time you are running them.

Hi all,

thanks for your answers and advice. Indeed SSD is very expensive these days but so is a new Mac (and it's a M4 dated 2024....).

So I would like to try this first.

But I also ran the etresoft tool and I am confused now. It says my harddrive is 'full' but when I open system setting and go to 'storage' I see that just about 70% of the 1TB is used and more than 300Gb free to use. That doesn't match according to me.

When I run the disk utility tool / first aid, I see several drives. I don't understand that part but running first aid reports no problems.

I added the etresoftsoft report here, so I hope you can figure out it there is a problem with the drive or not.

I indeed have Time Machine running on an (also pretty old) Synology but for some reason it did not connect anymore a long time ago. I could't solve it so I started a new Time Machine backup on the synology (space enough there).

I understand now that this may cause (a part of) the slow working iMac. So I must somehow get rid of the not working Time Machine archive first.

You write about OneDrive, I'm not aware of being connected to OneDrive or was it just an example

nldre wrote:

I indeed have Time Machine running on an (also pretty old) Synology but for some reason it did not connect anymore a long time ago. I could't solve it so I started a new Time Machine backup on the synology (space enough there).

I understand now that this may cause (a part of) the slow working iMac. So I must somehow get rid of the not working Time Machine archive first.

You shouldn’t be getting local snapshots with an active NAS connection.

Time Machine isn’t likely to directly degrade performance, it’ll fill local storage with backups (“available” versus “free’) when the NAS archive storage is unavailable.

Main storage getting full, however, can degrade performance.

You write about OneDrive, I'm not aware of being connected to OneDrive or was it just an example

OneDrive and Dropbox are both loaded and running. Whether they’re connected and actively transferring data, I can’t tell. Some file sync services can get chatty.

nldre wrote:

Here some screenshots in addition to the report. To me it looks like there are several drives present.

The internal drive section is about what I would expect for any Mac running Big Sur, or later, that did not have a Fusion Drive. Here's what my Mac, running Sequoia on a SSD, shows in Disk Utility.

Keep in mind that in the Finder, and in most GUI applications, this is all presented as one drive: Macintosh HD.

Much of this complexity is due to Apple putting large parts of macOS inside a "signed, sealed, system volume", and then having the Mac run only off read-only startup-time snapshots of that volume. Every version of macOS since Big Sur has structured startup disks this way and even Catalina had some elements of this.

I don't see anything special in your screenshot that reflects the EXTRA complexity that a Fusion Drive "device" really is a software construct layered on top of a SSD and a partition on a mechanical hard drive. Which simply suggests that that layer of complexity is hidden at a lower level that even Disk Utility does not display.

Specially container 4 with Creedence, what is that?

Google Translate says that "Schijfkopieën" is Dutch for "Disk images". So I am guessing that you have an APFS disk image (.DMG) file mounted, and inside, there is a volume whose name begins with "Creedence11M6270".

Here some screenshots in addition to the report. To me it looks like there are several drives present.

Specially container 4 with Creedence, what is that?