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User profile for user: Globalksp
Globalksp Author
User level: Level 1
23 points

Internal SSD (AP0512M)...slow write speeds?

Hello,


I recently purchased a second hand 2018 15" MacBook Pro from a certified Apple reseller (specs in screenshot). I'm a digital tech in the photo industry and hard drive write speeds are quite important when shooting tethered to the computer.


I recently picked up a G-Tech Mobile Pro external SSD and ran a Blackmagic speed test on it as well as my internal SSD and have questions. Are advertised speeds never attainable in real world computing?


It seems the internal Apple SSD (AP0512M) has advertised read & write speeds of 3200MB/s & 2200MB/s, respectively.

The Blackmagic tests (5GB) returned speeds of 2626MB/s & 1835MB/s.


For the G-Tech external, advertised "transfer speeds" are 2800MB/s and the Blackmagic tests returned 2487MB/s & 2282MB/s (read & write).


Nothing else was running when the tests were performed and high performance graphics (dual graphics card) were enabled. A friend has a 2019 16" MBP with a similar configuration and tested at 2722MB/s & 2632MB/s (read/write).


I'm most concerned with the internal SSD's performance. What steps are there to troubleshoot bad cells / SSD health / etc. Or, is this normal performance?


Thanks.



Posted on Apr 24, 2021 11:10 PM

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User profile for user: HWTech
HWTech
User level: Level 9
60,380 points

Posted on Apr 25, 2021 6:49 PM

The "Composite Temperature" is Ok. DriveDx is incorrectly interpreting the temperature attribute. For example in the screenshot the current temp is 26C which is represented in the "Value" column as 74C (100 - 74 = 26C). The "Worst" value column is only reporting 74 (aka 26C) so that is well below the "Threshold" of 30 (aka 70C which is calculated by 100 - 30 = 70C).


Don't always trust the interpretation of these apps when checking the health of SSDs.


Now to address your original question about SSD performance. The boot drive will always report slower than maximum speeds for multiple reasons. For one macOS is constantly reading & writing from/to the boot drive which is going to cause a performance hit. Plus the SSD will be performing its own maintenance & garbage collection routines including TRIMming the SSD. It is not unusual to see write speeds at half of the rated speed. If you were to erase the SSD and perform the same test while booted to an external drive you would most likely see speeds closer to the rated speed, however, even then the speeds can become slower once the SSD's write cache is exhausted which can occur in as little as 30 seconds for some SSDs when writing large amounts of data.


Your SSDs are working and performing properly from everything you have posted here.


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User profile for user: HWTech
HWTech
User level: Level 9
60,380 points

Apr 25, 2021 6:49 PM in response to Globalksp

The "Composite Temperature" is Ok. DriveDx is incorrectly interpreting the temperature attribute. For example in the screenshot the current temp is 26C which is represented in the "Value" column as 74C (100 - 74 = 26C). The "Worst" value column is only reporting 74 (aka 26C) so that is well below the "Threshold" of 30 (aka 70C which is calculated by 100 - 30 = 70C).


Don't always trust the interpretation of these apps when checking the health of SSDs.


Now to address your original question about SSD performance. The boot drive will always report slower than maximum speeds for multiple reasons. For one macOS is constantly reading & writing from/to the boot drive which is going to cause a performance hit. Plus the SSD will be performing its own maintenance & garbage collection routines including TRIMming the SSD. It is not unusual to see write speeds at half of the rated speed. If you were to erase the SSD and perform the same test while booted to an external drive you would most likely see speeds closer to the rated speed, however, even then the speeds can become slower once the SSD's write cache is exhausted which can occur in as little as 30 seconds for some SSDs when writing large amounts of data.


Your SSDs are working and performing properly from everything you have posted here.


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User profile for user: Globalksp
Globalksp Author
User level: Level 1
23 points

Apr 24, 2021 11:48 PM in response to Jack-19

Thanks for staying with this, Jack.


Gave it a read and makes sense. I've always been aware of temp throttling and keep constant tabs on my machines and up the fan controls to curtail any potential overheating. The machine does do a lot of intense processing of images for hours on end, but the fans are running at full clip while that's happening.

Here's where temps were at when DriveDX was refreshed (degrees Fahrenheit):

For anyone who finds this in the future and is wondering, this is what DriveDX has to say about composite temp:

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User profile for user: HWTech
HWTech
User level: Level 9
60,380 points

Apr 25, 2021 7:35 PM in response to Globalksp

I am glad to share what little I know to help others. I believe information should be freely shared so others can learn & understand more quickly so they can build upon the base. It is sometimes very hard to gather this information from anywhere online. I spent years piecing together this information through researching and also by observing and experimenting with our organization's SSDs. More websites have bits of this information today, but you still must dig to really find it and I'm not sure any site really has it all in one place. I have personally found most techs I speak with have even less of an understanding than I do which shows the terrible state of easily accessible and accurate information for some things like this.

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Internal SSD (AP0512M)...slow write speeds?

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