iMac 27 is extremely slow despite replacing HDD with SSD

I see 2 major items.

First is CMM is still installed, that needs to be fixed first. Please download FindAnyFile and have it search for:

• CleanMyMac
• MacPaw

and ensure all of the offending files are moved to the Trash and the Trash is emptied.

Next the report indicates your HD is failing. I strongly recommend that you use an external SSD to replace your hybrid Fusion system. Directions for setting up an external SSD are in How to setup an external SSD as your startup disk. The external SSD I recommend that you use is a OWC Envoy Pro SX. This will dramatically improve performance. If you do not feel comfortable doing this, then please contact an independent Apple Authorized Service Provider and they will assist. Genuine Apple Stores will not do this type of work. If you don't know of any AASP's in your area please click Apple Authorized Service Provider Locator (AASP) & Genius Appointment to start finding one.

First uninstall CMM. One-size-fits-all tools have a bad habit of inflicting collateral damage and CMM in particular has one of the worst reputations.

Second install and run Etrecheck, a diagnostic report aggregator. Post the report using the 'additional text' posting option. That will give us a better idea what is going on to recommend a specific solution.

padams35 wrote:

The BX500 may be slow by SSD standards, but it should still be significantly faster than your old HDD. Let us know if splitting the fusion drive fixes your performance issues or if slow performance persists.

I can tell you from personal experience the Crucial BX500 series SSDs are total junk. They overheat very easily and slow down to a crawl after writing data to it for more than 30-40 seconds once the SSD's write cache has been filled. It can take hours of rest before the SSD's speed may return to normal. I have also found the BX500 SSDs to have an extremely high rate of failure usually with very little use.....some of them have even failed right out of the box. You could not even pay me to use this SSD, that is how bad they are.

I've used Crucial SSDs for years for my organization without any major issues until my organization started to use the BX500 series SSDs.

The OP would do well just to replace the BX500 SSD with an MX500 SSD. The OP could have probably gotten the repair shop to replace it with an MX500 SSD for a slight increase in price for the higher end SSD if they had gone back right away. It is probably be too late now to have it replaced with an upgrade by the repair shop without significant cost. I'd be surprised if the SSD's temperature has not been at or even exceeded the critical temperature of 70C at some point where the SSD would experience thermal throttling. That is about the only thing that will show up in the SSD's health report which would indicate I may be correct. Unfortunately any other type of slow downs won't show up in the SSD's health report since it is just the SSD working as designed (poorly).

No need for the command line. Within Disk Utility just select the whole physical SSD to erase. See this Apple article for details:

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

Carol Hammal wrote:

Hi padam35,

So I did manage to split the fusion successfully and then erase both parts and reinstall Mac OS.

To my great surprise, now the Mac is even slower than when I had tried to erase & reinstall before the fusion splitting. It's oh so so so slow to startup (taking so far 5 min to restart) and it had also gotten stuck on the "setting up your account" for over 15 min during the setup phase. I had to quit that process.

I'm clueless at this point and this is becoming more and more frustrating...

My Crucial experience was with the BX300. Which worked well enough. However this is starting to sound like HWTech and the others are correct that the BX500 is a downgrade significantly worse than benchmark test results online indicate and the root cause of your problems.

Two final options:

a) Take the computer back to the Apple Store that installed the BX500, show them the slow performance, request a warranty replacement, and offer to pay the difference to buy-up to a better SSD such as the MX500. They probably won't since the SSD is working, but maybe they will.

b) Switch to using an external SSD as your boot drive. Buy yourself a USB-C SSD with a read speed of 900MB/s+ and follow these instructions: Use an external SSD as your startup disk … - Apple Community

P.S. To restore the fusion drive go back to command-R MacOS Recovery, go back to Utilities->Terminal, and run:

"diskutil resetfusion"

What rkaufmann87 about CMM / MacPaw.

For anyone else with CMM installed, use the vendor's uninstall script. (https://cleanmymac.com/faq/how-to-uninstall-cleanmymac ) Manual deletion also works, but is more complicated than drag/drop to trash.

Also it looks like the installer then fused your old well worn 28GB SSD fusion drive component with the new 512GB SSD. I suspect the mismatch is creating problems and would recommend splitting the drives apart and reinstalling MacOS back onto the new 512GB SSD.

1. Backup! Splitting the fusion drive will erase the drive contents. Make sure any data you want to save is on a working backup first. If the data is critical make a second backup.
2. Boot into recovery mode (Command+R)
3. Utilities -> Terminal
4. diskutil apfs deletecontainer disk2
5. Utilities -> Disk Utility
6. Erase/Reformat the two SSDs (GUID partition, APFS)
7. Reinstall MacOS
8. (Optional) restore date from timemachine backup or similar.

rkaufmann87 wrote:

Next the report indicates your HD is failing.

Actually the internal drive was replaced with a 500GB Crucial BX500 SSD which is an awful SSD (Crucial should be embarrassed to ever have made it as it tarnishes their reputation for quality & reliability). Have whoever installed that Crucial BX500 SSD replace it with a quality Crucial MX500 series SSD. The Crucial BX500 series SSD is a low end budget economy model that is as slow as a hard drive, overheats easily, and has an extremely high rate of failure.

The Crucial MX500 series SSD is Crucial's top of the line model for 2.5" models and is a good choice for price & performance.

I would rethink your choice of repair shops if it was their choice to actually use the BX500 SSD.

Carol Hammal wrote:

I went to Tradeline which is the one that has the highest status here and supposedly has the best and most reliable repair center.

Realizing that they're using cheap components truly makes me wonder about what else they're failing to do properly under the name of Apple.

Crucial is usually a very good brand, but like everyone else these days they decided to make a sub-par product to compete in the budget market space since so many people don't want to pay for things these days. It is possible the techs really don't realize how bad the BX500 SSD really is. Hopefully if you point it out to them they will replace it with a Crucial MX500 series SSD instead.

The techs can easily test the BX500 SSD to confirm what I am saying regarding its poor performance by writing data to the SSD non-stop for two minutes...even longer will really show how bad it performs & will likely show it overheating as well, but two minutes will probably suffice. They can easily check the SSD temperature by using an app such as DriveDx (free trial period) to check the SSD's SMART health attributes which includes a temperature value (may even include a temperature history as well if they use the command line to access that information through the "smartctl" utility within DriveDx and many other such apps). IIRC, the critical temp is 70C, but it has been some years since I examined the BX500 SSD closely. Other system temperature monitoring utilities (Macs Fan Control -- free) may also include the SSD's temperature, but only a drive specific app will have the ability to show the temperature history using the command line utility.

It they are a truly reputable repair shop, then they should be grateful for you to helping them identify a problem with their repairs which is easily correctable by them (both for you and their other customers). The price difference between the two SSDs usually is not too great although it can vary by region & supply. Just be courteous about it so they don't go on the defensive. Hopefully they will make it right for you.

Good luck.

Correct, entering "diskutil apfs deletecontainer disk2" as written into terminal (opened from recovery mode utilities) will usually delete a fusion drive and should be correct for you per the disk topography reported by etrecheck. (This might not be required if you erase/reformat both the small and large SSD)

When you next erase each drive in disk utility make sure "APFS" is selected as the new Format and "GUID partition" is selected as the new scheme.

The BX500 may be slow by SSD standards, but it should still be significantly faster than your old HDD. Let us know if splitting the fusion drive fixes your performance issues or if slow performance persists.

padams35 wrote:

My Crucial experience was with the BX300. Which worked well enough. However this is starting to sound like HWTech and the others are correct that the BX500 is a downgrade significantly worse than benchmark test results online indicate and the root cause of your problems.

Yes, the older BX series SSDs were actually Ok. The BX500 really tarnishes the Crucial brand.