Glacially slow old iMac; I've run out of ideas

[ScottR]

I have a Late 2014 27" Retina iMac. It's semi-retired (replaced by new Macs for everyday use) but still used periodically for various tasks.

Last week, without warning, it started to run unusably slowly. Rebooting didn't help; booting in Recovery and running Disk Utility didn't help (no errors), nor did Safe mode. Running Apple Diagnostics (booting holding down D) showed no errors.

I had a spare external drive with High Sierra on it (the iMac had Big Sur, the newest OS it could run). I booted off that and it ran much better, though still rather slowly--which I ascribed to using an older drive and USB 2.

I had noticed that the Fusion drive seemed to be split--oddly, into three drives, rather than what seemed to be the "normal" (for a split) two. After updating the external drive to Mojave I restored the split drive. That done, I installed Mojave (which I thought ought to run quicker than Big Sur) onto the newly restored and formatted Fusion drive and rebooted.

If it was any quicker, I couldn't tell. The simplest tasks were agonizingly slow.

So I ran Disk Utility again, both when booting off the external drive and in Recovery mode. No errors at all. I ran Apple Diagnostics again; no errors.

I've been working on this for days so I'm probably forgetting some of the steps but that's the gist. I'm at a loss. I'd replace the internal drive but I don't know for sure that's the issue (i.e., maybe a drive controller separate from the Fusion drive). Any other steps?

 

[Andrey84]

I have a Late 2014 27" Retina iMac. It's semi-retired (replaced by new Macs for everyday use) but still used periodically for various tasks.

Last week, without warning, it started to run unusably slowly. Rebooting didn't help; booting in Recovery and running Disk Utility didn't help (no errors), nor did Safe mode. Running Apple Diagnostics (booting holding down D) showed no errors.

I had a spare external drive with High Sierra on it (the iMac had Big Sur, the newest OS it could run). I booted off that and it ran much better, though still rather slowly--which I ascribed to using an older drive and USB 2.

I had noticed that the Fusion drive seemed to be split--oddly, into three drives, rather than what seemed to be the "normal" (for a split) two. After updating the external drive to Mojave I restored the split drive. That done, I installed Mojave (which I thought ought to run quicker than Big Sur) onto the newly restored and formatted Fusion drive and rebooted.

If it was any quicker, I couldn't tell. The simplest tasks were agonizingly slow.

So I ran Disk Utility again, both when booting off the external drive and in Recovery mode. No errors at all. I ran Apple Diagnostics again; no errors.

I've been working on this for days so I'm probably forgetting some of the steps but that's the gist. I'm at a loss. I'd replace the internal drive but I don't know for sure that's the issue (i.e., maybe a drive controller separate from the Fusion drive). Any other steps?

A good way to test if your HDD is starting to fail - and it really is expected to start failing by now - will be to get a new fast external SSD drive and try and boot off that. You can later return it via Amazon. If that's significantly faster, you have your answer. I'd do this as my first step.

 

[Mr_Brightside_@]

It’s the Fusion Drive. Purchase a usb 3 SSD (or Thunderbolt 2 but those are hard to find), clone the drive to it using carbon copy Cloner, and enjoy your better than new Mac.

 

[Fishrrman]

Thread title:
"Glacially slow old iMac; I've run out of ideas"

MY "idea":
Time to start shopping for a replacement.

At ten years old, there's nothing you can do that will bring it up to modern specs and speeds.

It sounds like your fusion drive is on the verge of failure.
Could be the platter-based HDD portion.
Could be the SSD portion.

Having said that..

Is the external boot drive you have an SSD, or is it a platter-based HDD?

You CAN "liven it up" by getting a USB3 SSD (I recommend the Crucial X9), using SuperDuper to "clone" the contents of the internal drive over to it, and then set the external SSD to become your new boot drive.

That will give it more speed. A USB3 drive will yield read speeds around 400-420MBps.
What kind of speeds are you getting NOW?
Check them and post your reply.

But again, you can't expect to transform a 10-year-old Mac into "something new".
It is what it is.

 

[ScottR]

But again, you can't expect to transform a 10-year-old Mac into "something new".
It is what it is.

Like I said, I already have a couple of new Macs; I'm just trying to keep the old one working for odd tasks (e.g., monitoring my security cameras, throwing video to an attached large screen TV, etc.). I never said I want to transform it into something new.

 

[DeltaMac]

Because you did not see any improvement after resetting the fusion drive, I suspect one of the two devices that make up the fusion drive is (probably) failing. And, it is entirely possible that if one of the internal storage devices is not working properly, that may even be affecting performance of an external device, too. And, that problem may simply be resulting in low performance, yet still pass the built-in diagnostic test. The situation remains--something about the internal storage, either the spinning HDD, or the SSD (flash storage) parts of the fusion drive are simply no longer performing to the level that you expect.
I would: remove both the HDD and the SSD, and probably replace the SSD with a new, larger capacity, NVMe card (a faster device than an SSD replacement for the internal SATA drive (the HDD)
Big project, and you have to be careful not to damage a fragile connector or two. But, the end result should give you the performance that you expect, and likely better performance than you have ever seen on this iMac. And, only you can decide if the work is worth the result for you (Is it worth your time to upgrade a 10-year-old Mac? if it serves a purpose for you, is it worth the effort (and your money) to make it work better?)

 

[Nguyen Duc Hieu]

I have a Late 2014 27" Retina iMac. It's semi-retired (replaced by new Macs for everyday use) but still used periodically for various tasks.

Last week, without warning, it started to run unusably slowly. Rebooting didn't help; booting in Recovery and running Disk Utility didn't help (no errors), nor did Safe mode. Running Apple Diagnostics (booting holding down D) showed no errors.

I had a spare external drive with High Sierra on it (the iMac had Big Sur, the newest OS it could run). I booted off that and it ran much better, though still rather slowly--which I ascribed to using an older drive and USB 2.

I had noticed that the Fusion drive seemed to be split--oddly, into three drives, rather than what seemed to be the "normal" (for a split) two. After updating the external drive to Mojave I restored the split drive. That done, I installed Mojave (which I thought ought to run quicker than Big Sur) onto the newly restored and formatted Fusion drive and rebooted.

If it was any quicker, I couldn't tell. The simplest tasks were agonizingly slow.

So I ran Disk Utility again, both when booting off the external drive and in Recovery mode. No errors at all. I ran Apple Diagnostics again; no errors.

I've been working on this for days so I'm probably forgetting some of the steps but that's the gist. I'm at a loss. I'd replace the internal drive but I don't know for sure that's the issue (i.e., maybe a drive controller separate from the Fusion drive). Any other steps?

I would suggest erasing the internal drive, unmount them for good and boot your iMac 2014 from an external SSD. USB 3.0 to save cost. That's all you need to cure the iMac slowness and repurpose it for common tasks.
You can also sell or donor it to people who don't have high demand on computing tasks. 2014 iMac are still very useful to many people.