External Thunderbolt HDD being identified as an Internal PCI-Express SSD

Larry Williams wrote:

I purchased a Samsung SSD 870 EVO 4TB to replace the drive.

The other thing that appears to be weird is when I test the speed of the old and new drives, the SSD has read/write speeds of 530MB/s and the old HDD, connected through thunderbolt, has read/write speeds of 2,500MB/s and 1,700MB/s.

I have a second drive in the OWC enclosure. It shows as being connected via SATA. This gets a read/write speed of only 230/293 MB/s.

4/ Why is the SSD speed so much slower than the old drive? Did I format the SSD incorrectly?

I can shed some light on SOME of your questions.

The Samsung SSD 870 EVO 1TB should work fine for you (despite what others might be saying about it). I have one in a 2015 iMac and it has been working fine. It replaced the original drive which was a mechanical HDD.

The Samsung SSD 870 EVO 1TB is rated for 530 MB/s via SATA and when I test it with Blackmagic Disk Speed Test I see 530 MB/s. An Apple Authorized Service Provider installed it for me and they said they see good results with that drive in Macs and they have a good reliability record. On Amazon there are over 19,000 customer ratings and it gets a solid 5 stars. To me that means more than someone denigrating it in these forums from some anecdotal experience in the past.

The second drive getting 230/293 MB/s is no doubt a different model/type, you should look up its specs to see if it is normal. SATA speeds are typically 500 MB/s or slower.

The other drive getting 2500 MB/s ... not sure why that is but note that your Thunderbolt 3 ports are rated for up to 40 Gb/s which is about 3200 MB/s, which is close to what you say you measured. So that might be ok also. I am guessing that the test when run is using the SSD part of the fusion drive, not the much slower HDD part. If it were using the HDD part I think you would see speeds less than one tenth of what you measured. Since there is an SSD portion of the fusion drive, it might show up as "SSD" in the profiler.

Try testing the drives by actually copying some large files. I think you will see up to about 500 MB/s for the Samsung SSD (that's what I see) but for the old fusion drive (HDD/SSD combination) I expect you will see closer to 100 MB/s to actually copy a large file.

So what you are seeing might all make sense.

Larry Williams wrote:

I had to replace the 3TB internal Apple Fusion drive due to Smart errors.

I purchased a Samsung SSD 870 EVO 4TB to replace the drive. I then placed the old drive (Seagate Desktop HDD 3TB) into an external OWC ThunderBay 6 enclosure with Thunderbolt 3 ports.

When I open Disk Utility the old drives appears under "Internal". When I bring up the details of the drive it identifies the connection as PCI-Express and Solid state as Yes?

The other thing that appears to be weird is when I test the speed of the old and new drives, the SSD has read/write speeds of 530MB/s and the old HDD, connected through thunderbolt, has read/write speeds of 2,500MB/s and 1,700MB/s.

I have a second drive in the OWC enclosure. It shows as being connected via SATA. This gets a read/write speed of only 230/293 MB/s.

So here are my questions:

1/ Why does the old drive show as being connected via PCI-Express and not as SATA like the second drive in the enclosure?

2/ Why does Disk Utility identify the old drive as being internal and SSD?

3/ Why are the read/write speeds so high and not comparable to the second drive in the enclosure?

4/ Why is the SSD speed so much slower than the old drive? Did I format the SSD incorrectly?

Speed testing was done using Techtool Pro (latest version)

System: MacOS Monterey 12.4

Mac: iMac (Retina 5K, 27" 2017)

Were there not issues with Samsung SSD 870 EVO and Mac compatibility...(?)

see if there is anything here: Samsung 870 EVO just won't work - Apple Community

What does your Terminal.app see...

diskutil list external

compare

diskutil list internal

I think macOS is still seeing the Fusion Drive even though the 3TB hard drive is now external because most likely the Fusion Drive is using the UUID of each drive to build/connect the Fusion Drive. The slow internal Apple original SSD's slow speed would be consistent with a Fusion Drive.

If the hard drive is failing, then you may not be able to recover the data from it depending on the severity of the failure since macOS and standard apps are unable to handle the errors produced by a failing drive and attempts can make the drive failure worse to the point even an expensive professional data recovery service will be unable to recover any data.

You should always have frequent and regular backups of your computer and all external media (including the cloud) which contains important & unique data.