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iMac 2019 i9 1TB SSD question

N

nkurtar

macrumors member
Original poster
Sep 13, 2019
47
13
Istanbul, Turkey
I got an iMac 2019 i9 Vega48 with 1 TB SSD. I have had it for 1 month. One thing drew my attention about SSD such that after booting if I run blackmagic disk test I get slow results like 1600 MB/s for reading and 1700 MB/s for writing. As the test keeps running test results get faster. After 10 to 20 wrlte and read cycle the results get to what they are supposed to be something like 2500 MB/s reading and 1800 MB/s writing. What could cause this behaviour of my SSD?
 
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I have a 2019 Core i9 iMac with the 1 TB SSD as well. I just ran Blackmagic Disk Speed Test and got the same type of results with slower speeds to start out with and then back up to the normal higher expected speeds after about 20 or so runs. The only thing I can think of is it has to do with the read/write cache size on the drive itself, or on the disk be tested.

DiskSpeedTest.png
 
Same here, i9 w/1TB SSD & Vega 48 and similar test results that get better with more runs. Curious.
 
Maybe there's things in the background going on after a restart that slow the performance. And if you re-run the test, the SSD "learns" that this app is SSD intensive and prioritizes that?
 
One other thing: It doesn't matter whether you just booted up or some time after boot. 20 or more has to run to get higher results. I tried other disk speed test AJA. The results are same as Blackmagic. By the way you guys which macOS version are you running on?
 
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nkurtar said:
One other thing: It doesn't matter whether you just booted up or some time after boot. 20 or more has to run to get higher results. I tried other disk speed test AJA. The results are same as Blackmagic. By the way you guys which macOS version are you running on?
Click to expand...

Catalina 10.15.1
 
same here. I have a 2019 Imac hexacore with 256gb ssd. With mojave the ssd speed was 2500Mb/s reading and 1500Mb/s writing. now after catalina update the speed is 1700Mb/s reading and 1400Mb/s writing.
i had problems with boot too: after the first update the complete boot had required 46s!!! with the catalina 10.15.1 update the boot problem was fixed (32s).
I hope that the slow ssd speed will be fixed with future updates
 
Sisti00 said:
same here. I have a 2019 Imac hexacore with 256gb ssd. With mojave the ssd speed was 2500Mb/s reading and 1500Mb/s writing. now after catalina update the speed is 1700Mb/s reading and 1400Mb/s writing.
i had problems with boot too: after the first update the complete boot had required 46s!!! with the catalina 10.15.1 update the boot problem was fixed (32s).
I hope that the slow ssd speed will be fixed with future updates
Click to expand...
I hope so...
 
I have a question for you when you check your HD (SSD) in the 'About this Mac' menu what kind of disk you get? I ordered an iMac 27 with a 512 SSD but it is listed as "Flash Storage", is that right?. I have another Mac and the SSD is listed as SSD so...
 
sleeper22 said:
I have a question for you when you check your HD (SSD) in the 'About this Mac' menu what kind of disk you get? I ordered an iMac 27 with a 512 SSD but it is listed as "Flash Storage", is that right?. I have another Mac and the SSD is listed as SSD so...
Click to expand...
Just to chime in; my Mac Mini 2018 has also its SSD listed as Flash Storage. All is well :)
 
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