iMac SSD vs SSD part of 2TB

probak

macrumors newbie
Original poster
Jun 26, 2009
6
1
Hi,

I need to make a choice. There are three possibilities:
1. iMac 2015 with 2TB Fusion Drive
2. iMac 2017 with 256GB SSD
3. iMac 2017 with 2TB Fusion Drive

My assumption is to split Fusion Drive into 2TB HDD & 128GB SSD. To me 128GB SSD would be enough to put there system + Lightroom catalog... and move home folder to 2TB drive.

BUT how fast is 128GB part of 2TB Fusion drive? I couldn't find the answer to this question... can anyone help? :)
Ideally we could compare benchmarks of 128GB SSD part of both 2015 & 2017 version + 256SSD of 2017'
 

007 Junior

macrumors regular
Apr 15, 2013
144
107
The Netherlands
Your Mac sees the Fusion Drive as one physical hard drive. This means that not you, but macOS decides which files will be on the SSD part and which files on the HDD part of the Fusion Drive. If you want complete control over your storage, I would definitely recommend going for pure SSD storage.
 

probak

macrumors newbie
Original poster
Jun 26, 2009
6
1
Exactly!

I'd prefer 2TB HDD & 128GB SSD if.... SSD is at least around 1000MB read/write speeds... is it? ;)
 

ljeffs

macrumors member
Oct 14, 2004
39
9
Victoria, Australia
This is my 2017 iMac 3.8GHz i5 2TB Fusion Drive. I was hoping write speed would be up with the read like it's straight SSD brothers, but it doesn't seem to be the case:
DiskSpeedTest.png


Update: I have seen the write speed go up to 750 MB/s but the write test results fluctuate between 550-750, so the picture is a fair average.
 
Last edited:

probak

macrumors newbie
Original poster
Jun 26, 2009
6
1
ljeffs, thanks for the screenshot!

So it means that 128GB part of 2TB Fusion Drive is at least that fast!
ljeffs, I bet you don't have time to split Fusion Drive and test it again ;)

anyone? :)
 

ljeffs

macrumors member
Oct 14, 2004
39
9
Victoria, Australia
No, I don't feel the desire to delete my internal storage... ;)

There is a screenshot in another thread which shows the write speed as good as the read for the straight SSD. So with this showing the write speed is much worse, it has me second guessing that I should of went with the 512GB SSD...:(
 

probak

macrumors newbie
Original poster
Jun 26, 2009
6
1
Imagine: maybe Blackmagic was (by chance!) reading from SSD part and writing... partially to HDD & SSD!
It could explain 2200/675

If it's the case: you need to destroy Fusion Drive structure, install Sierra again and test the speed of pure SSD :)

Jokes apart: I hope there is someone who already did this job and could share the results...
 

probak

macrumors newbie
Original poster
Jun 26, 2009
6
1
So... I had to order new Mac to test these speeds... Here we see the results of SSD and HDD part of Fusion Drive 2TB
 

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