User profile for user: rtoledof
rtoledof Author
User level: Level 1
14 points

iMac 27" (2019) Fusion Drive slow, internal SSD upgrade?

I have an iMac 27'' from 2019 late. I had in the pass issue with my hard drive and I lost all the info I had on it because the disk for some reason was damage. Till now I have been working with it before I had the system installed in an ssd disk and it was working fine but it's an external disk. I started having some issue and came here and some one from here suggested me to install once more the system in my disk what I did. Recently I started experimenting a big issue with slowness in the IMac once more and I try the BlackMagic Disk Speed test that is in the Apple Store and to my surprise the read and write speed of the internal disk on the iMac is lest than 50 mb/s what is a really bad read and write speed but this iMac was not designed to use a SSD disk instead is using a Fusion Drive what looks like was not the good apple was thinking it is. Any suggestion of how I can make the possibility to install an internal SSD in this model of iMac to improve the speed on it? The iMac is a little old I know but right now don't have the possibility to buy a new one and it's quite hard to work with it right now. I'll appreciate any suggestion that could be advice here.


Thanks for the help.

iMac 27″, macOS 15.7

Posted on Jun 18, 2026 7:05 AM

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User profile for user: Tesserax
Tesserax
User level: Level 10
160,106 points

Posted on Jun 18, 2026 7:34 AM

Based on the symptoms described, the most likely cause of the severe slowdown is a failure or degradation of the hard disk portion of the Fusion Drive. The reported read/write speeds of less than 50 MB/s are significantly below what would be expected from the SSD portion and are consistent with a failing or degraded mechanical hard drive.


Before proceeding with hardware replacement, I suggest the following be performed:

  • Verify the health of the Fusion Drive using Disk Utility (First Aid). Test both the SSD & HDD portions of the drive.
  • Use DriveDx to both review SMART status and confirm whether the SSD and HDD portions of the Fusion Drive are both detected correctly.
  • Ensure a complete backup of all important data is available.


Your iMac can be upgraded by replacing the internal hard drive with a single SATA SSD. This is generally the most effective way to restore performance and improve reliability. Three that I would suggest are: Samsung 870 EVO, Crucial MX500, or Western Digital Blue SA510. No matter which you actually go with, I further suggest that you get one in either the 1 TB - 2 TB range.


The basic replacement process would include:

  • Create a complete backup of all data.
  • Open the iMac by removing the display assembly. Because the display must be removed to access the internal storage, this repair requires specialized tools and replacement display adhesive strips. If you're not comfortable performing the repair, I suggest having the SSD installed by an authorized service provider or an experienced Mac repair technician.
  • Remove the existing Fusion Drive components.
  • Install a compatible internal SSD.
  • Reassemble the iMac and replace the display adhesive.
  • Reinstall macOS using Internet Recovery or a bootable installer.
  • Restore your data from backup.


IMPORTANT CONSIDERATIONS

  • A 2019 iMac is now considered "Vintage" by Apple Support. That means, getting repairs or replacement parts will be near impossible.
  • The Mac's operating system cannot be upgraded beyond macOS Sequoia 15.x. Apple typically only supports the latest three versions (currently: Tahoe, Sequoia, & Sonoma) for security fixes. Golden Gate, which is in beta, should be coming out later this year. That will drop Sequoia to "third place". Meaning? Your Mac has about one more year before it will no longer receive macOS updates.
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User profile for user: Tesserax
Tesserax
User level: Level 10
160,106 points

Jun 18, 2026 7:34 AM in response to rtoledof

Based on the symptoms described, the most likely cause of the severe slowdown is a failure or degradation of the hard disk portion of the Fusion Drive. The reported read/write speeds of less than 50 MB/s are significantly below what would be expected from the SSD portion and are consistent with a failing or degraded mechanical hard drive.


Before proceeding with hardware replacement, I suggest the following be performed:

  • Verify the health of the Fusion Drive using Disk Utility (First Aid). Test both the SSD & HDD portions of the drive.
  • Use DriveDx to both review SMART status and confirm whether the SSD and HDD portions of the Fusion Drive are both detected correctly.
  • Ensure a complete backup of all important data is available.


Your iMac can be upgraded by replacing the internal hard drive with a single SATA SSD. This is generally the most effective way to restore performance and improve reliability. Three that I would suggest are: Samsung 870 EVO, Crucial MX500, or Western Digital Blue SA510. No matter which you actually go with, I further suggest that you get one in either the 1 TB - 2 TB range.


The basic replacement process would include:

  • Create a complete backup of all data.
  • Open the iMac by removing the display assembly. Because the display must be removed to access the internal storage, this repair requires specialized tools and replacement display adhesive strips. If you're not comfortable performing the repair, I suggest having the SSD installed by an authorized service provider or an experienced Mac repair technician.
  • Remove the existing Fusion Drive components.
  • Install a compatible internal SSD.
  • Reassemble the iMac and replace the display adhesive.
  • Reinstall macOS using Internet Recovery or a bootable installer.
  • Restore your data from backup.


IMPORTANT CONSIDERATIONS

  • A 2019 iMac is now considered "Vintage" by Apple Support. That means, getting repairs or replacement parts will be near impossible.
  • The Mac's operating system cannot be upgraded beyond macOS Sequoia 15.x. Apple typically only supports the latest three versions (currently: Tahoe, Sequoia, & Sonoma) for security fixes. Golden Gate, which is in beta, should be coming out later this year. That will drop Sequoia to "third place". Meaning? Your Mac has about one more year before it will no longer receive macOS updates.
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User profile for user: rtoledof
rtoledof Author
User level: Level 1
14 points

Jun 18, 2026 8:19 AM in response to Tesserax

I'm currently in Poland and I was calling some of the Authorised services from Apple and they say that they can't perform the replacement if I'm bring in the SSD to them.


It's unbelievable that Apple just don't cate about the old products that they had and the in case I want to recycle this iMac at this time they will will pay less that 1k PLN for an iMac that cost 10k. I'll have to find a no Authorised service to do the replacement or buy the tools and made the replacement by my self. Even if I don't want my iMac any more be protected I can't do the replacement in and Authorised service. That's sad it's like you are sending your Gradpa to a place where some one else will take care of him without you to ve involved in the process.


Thanks @Tesserax for the detailed explanation, now will check with some one that could made the replacement of the disk or do it my self.


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iMac 27" (2019) Fusion Drive slow, internal SSD upgrade?

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