Advice on upgrading from 10.12 Sierra to 10.14 Mojave (2017 iMac)

[kiwidesign]

Hey all! I'll try to keep this as brief as possible

My parents' mac is a 2017 base 4k iMac (quad-core 3GHz i5, 8gb ram, 1TB Fusion Drive).
I don't visit them often, and while I do some basic maintenance from time to time, the machine has never been updated past 10.12.6 Sierra (I know, I'm a terrible son)

After 4+ years of continuous usage without a single reinstall, the iMac has become unreasonably slow in pretty much every aspect (and I suspect some of the blame is on the Fusion Drive not working as well as it initially did). While the obvious solution would be a clean install of a semi-modern OS, I don't currently have time for that, so I was wondering:

In your opinion, would and upgrade install to 10.14 Mojave (32 bit compatibility needed for some apps I don't currently have time to replace on their system) make the machine even slower, or could it possibly breathe some new life in this averagely-old machine? (just wishful thinking, but maybe the automatic APFS conversion during the update could freshen up the drive somehow)

Thank you very much!

 

[MBAir2010]

Mojave rules!
Sierra and high Sierra were bad on my MacBook air and mini
just time machine the Imac
and here is a Mojave Link in case you cant find one.

and here is the latest Mojave

 

[Aesthetica]

Don't quote me on it but I think only SSDs get updated to APFS by default, I don't think it works well on HDDs, so I assume the same might be true of Fusion Drives.

The real solution, while sadly not free, would be a USB-C SSD as the boot drive, which would make the machine feel brand new (2017 is still pretty new!)

 

[kiwidesign]

Don't quote me on it but I think only SSDs get updated to APFS by default, I don't think it works well on HDDs, so I assume the same might be true of Fusion Drives.

The real solution, while sadly not free, would be a USB-C SSD as the boot drive, which would make the machine feel brand new (2017 is still pretty new!)

Hey! About APFS just google it, High Sierra was the one lacking but Mojave added APFS support for Fusion Drives and I'm hoping it'll work well enough.

About your solution I gotchu: I already considered doing so, and since I've had good experience with this Sandisk drive I was thinking about buying one for my parents; I ran some benchmarks from their machine with the one I own, and they look decent. tbh I thought Thunderbolt 3/usb-c (above) would be much faster than the same drive via USB-A adapter (below) but I think the speeds are acceptable - I'm no expert though

Interestingly, when I tested the internal FD the speeds were crazy good, but it's pretty obvious that the entire benchmark ran on the SSD part of thr Fusion Drive:

I'm thinking I'm going to update install on the FD itself, and if they find the update slowed down the machine considerably, I'll buy the SSD and clone the system on it

 

[Fishrrman]

I doubt Mojave will run much "faster" than 10.12 Low Sierra on a fusion-drive equipped iMac.

It's not really the OS.
It's THE DRIVE that is slowing things down.

As you mentioned, an SSD will speed things up.

If the 2017 4k iMac has USBc ports, you can get the most speed by using a USB3.1 gen2 SSD. This will yield reads up around 800MBps or perhaps even a little more.

This will make a BIG difference and I predict your parents (and you) will be very pleased with the results.

You can either buy a "put-together" USB3.1 gen2 SSD (like the Samsung t7)
or
Get a "bare" nvme blade SSD, a USB3.1 gen2 enclosure, and put it together yourself.

Here's how I would do it:
a. get the SSD ready first.
b. use CarbonCopyCloner (free to download and use for 30 days) to create a cloned backup of the internal (with Low Sierra) to the SSD. Now you have a backup in case something goes wrong.
c. install Mojave onto the internal drive. You're going to have to get ahold of a copy of the Mojave installer, create a bootable USB flash drive from it (you'll need a USB3 flashdrive 16gb or larger).
Then, boot from the flashdrive installer, erase the fusion drive to APFS, then install Mojave "clean".
Then, use setup assistant to restore your parents' data during initial setup.

IF ANYTHING GOES WRONG... you STILL HAVE a bootable copy of your parents "old install" on the SSD as protection. That's why you took the extra time to make it, right...?

Hmmm.... where to get Mojave?
I've got just the source:

macOS Mojave Patcher

Download the free "Mojave Patcher".
Launch Mojave Patcher.
If you see an alert "this machine is already supported", just "click it away" (ignore it).
Now... look at the "tools" menu.
See "Download macOS Mojave".
Click that ... and you'll get a copy of Mojave.

To make the bootable installer:
I recommend either:
Diskmaker X (be sure to download the version intended for Mojave)
or
Install Disk Creator.
Both are free. Google them.

Either of these will make it a snap to create the bootable flashdrive with only a few clicks of the mouse.

Now you have a bootable Mojave installer.

Once you have Mojave up-and-running on the internal drive, with your parents' data restored, let them "run with it" for a week or so.
If "everything looks good", I would then erase the SSD to APFS, and again use CarbonCopyCloner to do a fresh clone of the fusion drive to the SSD.
Now... go to the startup disk pref pane and set the SSD to be the boot drive.
That should do it.

A lot written here.
Good luck.