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Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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Replace SSD, write speed is only 133.3MB/s, what is wrong?

Hello. I have imac 27" late 2012 with 3TB fusion drive. About 6 months ago I split my drive into separate drives 3TB HDD and 128MB SSD. I tested the ssd speed using BlackMagic.app, and the disk write speed was 237MB/s a read is 404.5 MB/s.

Today I changed the 3TB HDD for SSD 1TB Samsung 850 PRO. I tested the disk speed, disk write speed is only 133.3 MB/s and read is 519.8 MB/s.

I watched for several videos on youtube channels. All imac late 2012, that had changed drives for ssd, had write and read speeds of around 500 MB.

Why does my disc have a slow write? How to fix it?

Thank you MAJO

Update (03/11/2018)

Block Image

Write to disk is too slow. Here is print screen.

Answer this question I have this problem too

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Who's SSD did you install (Make, Model & Size)

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I replaced the Apple 3TB Seagate HDD and put in a Samsung 850 PRO SSD 1 TB (model MZ-7KE1T0)

I still have the second original SSD 128 MB.

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Lets make sure your new drive is your boot drive. Hopefully you've installed the OS on to it. Go to System Preferences > Startup Disk and make sure the Samsung SSD is set. Hows it look this time?

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Disk is set to boot drive. I did a clean install osx HighSierra on the SSD disk.

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Marian Brincko will be eternally grateful.
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