2019 iMac running very slowly after SSD replacement

a SATA SSD in the 2019 iMac SATA bay should be sustaining 450-500 MBs Read/Write

Black Magic or AJA speed apps are the proof

in my experience

the original Apple SATA cable should work in place on the new 2.5" SATA SSD

you don't need a 3rd-party cable, adapter or the temperature probe

only a 2.5" sled adapter to swap the original 3.5" SATA HDD in 27" 5k models

the 21.5" 4k iMacs come with 2.5" SATA hardware from Apple so no adapter sled is needed

i highly recommend the Samsung 870 EVO 2.5" SATA SSD -- as the SATA upgrade drive

i would return the Crucial -- based on the dismal speed performance alone -- and get the Samsung

hopefully you haven't sealed up your screen assembly yet because fresh adhesive is a pain to cut off -- be careful -- be very patient -- try using a thin plastic card to separate the seams now that you know where the tape gets fat

+++++

the so-called Fusion drive is only "fast" (1800 MBs write 2400 MBs read) when it's accessing the Apple SSD (NVMe SSD) -- it's a limited illusion -- 97 percent of the fusion is HDD (spinning disk) that maxes out at 80 MBs Read/Write

i.e., Apple's fusion is 3% SSD 97% HDD

in the long run SATA SSD is much faster than Fusion when fusion hits the HDD

SATA SSD is more than 5 times faster read/write than SATA HDD

Apple's SSD (NVMe) is 25 times faster read/write than SATA HDD

+++++

first I would try using Disk Utility to Erase the Apple SSD (format APFS) and use it for fast storage

it's possible the original Apple SSD still has the "fusion" formatting (you haven't reformatted it yet) and confusing the system that reformatting it may solve any conflict

or your System is bad

or your upgrade hardware is bad...

bobtimmons wrote:

My wife has a 2019 iMac with an Intel 3GHz i5 with 80GB of RAM and it's running terribly slow and has been for some time. I suggested we swap out the 2TB HDD with an SSD to see if that helps. As it turns out, the original spec was a Fusion Drive with a 128GB NVME drive along with the 2TB HDD. I removed the 2TB HDD and replaced with a 2TB SSD kit I got from iFixit. This included a Crucial SSD, SATA cable adapter and temperature probe. I got it all connected and, it's no better.

Even before looking at the DriveDx & EtreCheck reports I suspected you bought the BX500 SSD. Both @den.thed & @John Galt hit the nail on the head.

I took a quick look at the DriveDx report for the Apple NVMe SSD, but cannot really tell why DriveDx would report it as failing. If you look in Disk Utility, does that Apple SSD show "SMART Status Failed"?

Also, post screenshots of DriveDx for the Apple SSD. Resize the DriveDx window to allow as many of the health attributes to be seen in a single screenshot. Show the summary window & the health attribute chart windows. Maybe seeing the data in a different format will reveal why DriveDx flagged the Apple SSD.

If there really is a hardware issue with the Apple SSD, then there is a small chance it could also introduce performance issues. Most SSD failures occur due to the SSD's controller no longer communicating with the system which results in the SSD disappearing or in really bad cases, it may cause a huge performance issue while the computer/OS is trying to communicated with the bad SSD.....the latter has been rare in my own personal experience and would likely result in not being able to boot or use the system.

You can try installing macOS onto that Apple 120GB SSD just to see how things perform. You won't be able to do much more than that since a 120GB SSD can barely hold macOS and a few apps, but it would be a quick & easy way to test the system & that SSD. If you choose to try this, then once macOS boots to the Apple SSD, eject the BX500 SSD to prevent macOS from doing anything with it.

However, the majority of the drive related performance issues will be due to that BX500 SSD.

I agree witht the others that the Crucial BX serial has not played well with Macs based on user reports here. The MX seems far better. However, the BX might do better if you engage TRIMforce. Although some sellers say TRIM is not needed, I find with my Macs that have aftermarket SSDs that, without TRIM, the SSD can start to slow—often badly—over time.

Did your BX ever run fast?

This article explains how to enable TRIMforce. No disassembly required:

https://eshop.macsales.com/blog/31619-how-to-execute-trimforce-command-with-your-owc-ssd/

What the article does not tell you is what I learned with the help of our amazing Grant Bennet-Alder: you have to finish the job with a SAFE MODE Boot. The computer needs to "soak" in Safe mode for up to an hour after engaging TRIM for SAFE Mode to finish all its housekeeping before you do a normal restart and retesting the speed.

I installed an OWC SATA 6 SSD in my old Macbook Pro that kicked its drive scores from 75MB/sec for the slow factory mech HDD to 500MB/sec. OWC said TRIM was not needed. After 2-3 years the SSD speeds slowed dramatically, first to about half, eventually falling to old mech hard drive speeds—~60MB/sec.

It's easy enough to test. It is unlikely to cure your current issues but it may allow the iMac to run a little faster in "limp home" mode.

An external Thunderbolt SSD used to be an awesome performance boost but recent price increases for solid-state storage had taken the fun out of recommending it. The 1TB external SSD I bought for US$100 last March was up to $250 when I checked last week!

I think that -g is on to something here.

Where did you purchase that 2T Crucial BX500 SSD...?

Crucial's lower end BX500 SSD's have a bad reputation of not playing well when internally installed in Mac's.

Like -g, I also recommend that you replace that Crucial BX500 SSD with a Crucial MX, a Samsung, a WD or even a PNY SSD. I have personally used PNY SATA SSD's to upgrade Intel Mac's for years and have never had one fail yet. As those old Intel Mac fail and/or become useless, I pull the PNY SSD's and use them for redundant CCC backups.

While a SATA SSD will be slower than the NVMe SSD component of a 2019 iMac's Fusion Drive, it should not be "speed of a floppy slow."

In fact, if the Fusion Drive is a 1 TB Fusion Drive, the SATA SSD might well be faster than the Fusion Drive overall, because all of the real estate on it is "prime real estate"; whereas the 1 TB Fusion Drives shipped with 2019 Macs had a very small amount of SSD space compared to the original 1 TB Fusion Drives.

Here, the size of your Apple NVMe SSD implies that your 2019 iMac originally came with a 2 or 3 TB Fusion Drive. The fact that that SSD is failing may be significant. When the hard drive on my old iMac started failing (after I had already switched to using an external SSD), the drive would sometimes remount itself without being asked. Later, there were kernel panics even when the Mac was started up from the external SSD. So possibly, bad drives might be able to throw errors that crash or slow down a Mac even when those drives are not "in use".

If you open the Mac again, and replace the failed NVMe SSD with a compatible working one, I wouldn't recommend establishing a new Fusion Drive afterwards. Just leave the drives as two independent internal drives. But my guess is that if you open the Mac again, you'd probably just want to pull the NVMe drive and leave nothing in its place.

There are numerous reports on this site of the BX500 SSD being "pure and utter junk".

WindowsServer crashes and kernel panics… - Apple Community among many others.

Something seems funny here. DriveDX reported the information about the internal SSD under the heading "### DRIVE 1 OF 1 ###".

Did you run it only against the Apple SSD? Or is this an indication that you did not "break" the software linkage between the Apple SSD and the SATA drive, and the Mac somehow thinks that both are part of a Fusion Drive?

Maybe someone more familiar with Fusion Drives and with DriveDX can comment.

Allan Jones

>> old Macbook Pro that kicked its drive scores from 75MB/sec for the slow factory mech HDD to 500MB/sec. OWC said TRIM was not needed. After 2-3 years the SSD speeds slowed dramatically, first to about half, eventually falling to old mech hard drive speeds—~60MB/sec.

my experience -- i once favored OWC SATA SSDs (for about 5 years) but started having issues them -- one after another and OWC tech support was tedious and ineffective to deal with -- at one time i had about six of them -- i got rid of all of their SSDs -- i also had problems with Crucial and PNY SATA SSDs (got rid of those too)

these days i only buy Samsung SSDs -- they haven't been perfect either, but Samsung warranty is easy, fast and decisive replacing them -- you really need to watch the firmware on Samsung SSDs and keep them up to date -- bad firmware versions are what seem to kill Samsung SSDs

IF ANYONE USES SAMSUNG SSDs i recommend they check the firmware for any known issues and updates -- i've found a couple of the bad ones doing that -- Samsung will replace them. They will also pay shipping to send them the SSDs to flash the firmware to latest.

my recommended external enclosure is ACASIS TBU405 Pro (with the built in fan)

it supports Thunderbolt 3-4

they have a newer Thunderbolt 5 version, but it slows considerably (1000 MBs read/write) connected to TB 3-4 ports

Samsung 990 Pro NVMe SSD run (2300-2500 MBs) in the ACASIS thunderbolt 4 enclosure

earlier SSDs like the Samsung 970 EVO Plus run slow (1000 MBs write, 2500 MBs read) in external enclosures

though 970 EVO Plus run full speed internally mounted on the main board (2017-2019 iMacs)

WD_BLACK SN850X are my budget NVMe SSD -- I use them in external enclosures

WD_BLUE SN5000 also for redundant backups and storage -- not for boot drives

both these Western Digital SSDs run (2300-2500 MBs) in the Acasis via Thunderbolt 3-4

i am not sure how reliable these WD SSDs are in the long run, so far so good

PS

if you find yourself needing to cut the screen assembly back off -- take a moment's pause

NEVER PRY ON THE GLASS to separate the adhesive

don't use anything or any angles that will gouge the screen bottom or antennas

the cutting wheel reaches the thin areas (a lot stickier this time) -- but -- the three rectangular antennas will be your challenge points to re-separate because they rest deeper than the wheel can cut

i use a super thin plastic card (credit card size) to reach those areas, and cutting off fresh adhesive is a royal pain...

So "new 2019 Imac", without no ,Time Machine back-up?