M4 Pro - is it normal to have faster write speed than read speed?

[Astrohunter]

Hi,

As in title, also are these speeds good? It's a 1TB version.
In BlackMagic I selected the 1GB option.

 

[Astrohunter]

Same thing happens here actually:

 

[bassjunky]

Damn that's fast. I bought the M4 512GB version which gets about 3GB/s each way, write being a bit faster than read.

 

[Astrohunter]

Damn that's fast. I bought the M4 512GB version which gets about 3GB/s each way, write being a bit faster than read.

Apple doesn’t mention that lower SSD models are slower unfortunately.

 

[gilby101]

As in title, also are these speeds good? It's a 1TB version.
In BlackMagic I selected the 1GB option.

Oh yes, the speeds are good. But you won't see that sort of speed if you write 100 GB. SSDs have write caching. So initial writes are fast and suddenly slow when cache is filled. What you are seeing is the write speed to the cache. BlackMagic is not really very good for serious benchmarking. Some background https://eclecticlight.co/2025/03/17/why-ssds-slow-down-and-how-to-avoid-it/ Even though the examples are for external SSDs the principles still apply for internal SSDs. Apple don't publish details of their SSDs, though things like size of cache can be inferred from benchmarking with much larger amounts of data.

 

[Fishrrman]

Q:
"is it normal to have faster write speed than read speed?"

Back in the Intel Mac days, it was the opposite.
Read speeds almost always exceeded write speeds - sometimes by quite a lot.

BUT... Apple Silicon seems to have changed that.
Literally "swapped it around".
Now, write speeds edge out read speeds in most cases.

I have no idea why.
I'd like to hear a reasonable explanation of "why this is"...

 

[bzgnyc2]

Hi,

As in title, also are these speeds good? It's a 1TB version.
In BlackMagic I selected the 1GB option.

I would repeat with at least its 5GB option.

Depending on what your goals are, I would also test with AmorphousDiskMark.

Now that what you are seeing is bad -- just that it may not be representative of what the system will sustain under your workload.

 

[PaulD-UK]

If you test with the BlackMagic 1GB file size option you are testing the write speed to the cache, not to the storage NAND.
It’s better to test with a 5GB file size option, but even that isn’t going to exceed the cache size.