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A2115 / 2019 / Processors from 3.0 GHz 6-core i5, up to 3.6 GHz 8-core i9. Released March 19, 2019.

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Slow write TB3 EVO+ speed on iMac 2019 i9 vs 2018 MBP i7

What is the reason that the write speed with a TB3 Orico TCM2T3-G40 enclosure with a Samsung 970 EVO Plus 1TB installed is much slower on 2019 27” iMac i9 8 core (64GB, 2TB SATA SAMSUNG SSD, 128GB Blade SSD) than 2018 15” MacBook Pro i7, 6core, 32GB?

  • MacBook Pro: Write: 2200MB/s, Read 2550MB/s
  • iMac Write only 850MB/s, Read: 2500MB/s

Tried with APFS and EXFAT too - with same results.

Thank you!

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It’s what I would expect! Your source drive is likely the limiting factor.

You are hitting either the limits of the SATA interface 6.0 Gb/s of the 2 TB SATA Samsung SSD. You do have a faster SSD the PCIe/NVMe blade SSD, but its only 128 GB in size so that limits you on how much is holds of the test file/s.

So why is your 2018 MacBook Pro so much faster! Here Apple has done some magic which pushes the I/O to the limits on what the flash chips can run at. Unlike a typical M.2 PCIe blade SSD which uses a single channel to access each flash chip, Apple accesses each chip independently with its own I/O channel via its T2 chip controller.

Update (11/28/2020)

I set up lot of systems for video editing for both pro’s and students.

The ideal setup is to have a sizable performance drive internally as your boot drive. Here on your iMac that would be the PCIe/NVMe drive. For small production a 500GB is fine for large production a 1TB is strongly recommended. Here we set it up as the drive holding your OS & apps as well as set for the scratch space. Basically we want to leave a good portion of the drive empty! As your OS will leverage it for virtual RAM and caching.

The second drive (SATA) is your storage of your common elements for your production and your media.

If you can’t go with this setup your alternative is to use a high speed TB drive as your boot drive, basically setting it up like I described above. This won’t be as good as the internal solution but it will also work.

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Thank you Dan! Im not an expert, but I thought if I make speed test with the Blackmagic app, the speed of the "target drive" (in this case the external NVME Samsung 970 EVO Plus SSD on the TB 3 port) is depends only on the enclosure chip and the SSD speed and must be around the same values on each 2018-2019 laptop or desktop machines, because TB3 is on the PCIe bus in both case. How can I reach with iMac bigger speed on TB3? I have to change the factory blade SSD for a bigger one or because of the missing T2 chip is only a waste of money?

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The TB3 drive is limited by the ability of the data to be pumped to it. Your testing is moving data from A to B and then B to A, so the slowest drive/interface becomes the limiting factor and in some cases the lack of space..

Your iMac doesn't use a T2 chip so thats not an issue here.

As to what to do to get more performance it all depends on what your use case is. Can you explain what you are doing that would help in helping you on what direction you need to go with.

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I would like to speed up my video works with FCPX and spare space on the internal drives. I not really understand how can the internal SATA drive hold back the speed of the PCIe devices. Thank you so much your comments Dan!:.-)

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Peter zal eeuwig dankbaar zijn.
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