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