Believe in Blackmagic?

[Lettermanian]

Something that puzzles me, and I would appreciate knowledgeable insight: I have a Samsung T7 Shield SSD connected directly via usb-c to my M2 Mac Mini. According to Apple and Samsung, this combination should yield a max write/read speed of 1000 MB/s and 1050 MB/s. However, when I use Blackmagic's Disk Speed test app, the T7 consistently gets write speeds of about 1500 MB/s (and read speeds of about 700 MB/s, which is expected).

My question: why is the write speed consistently faster than what the connection should achieve? Does this mean that a drive like the T9 20GB might actually achieve those speeds? I thought the Mac's 3.1 Gen 2 USB-C had an upper limit of 10GB/s. Screenshots:

















--
The grass isn't always greener, unless you shoot Velvia.

 

[Greybeard2023]

Something that puzzles me, and I would appreciate knowledgeable insight: I have a Samsung T7 Shield SSD connected directly via usb-c to my M2 Mac Mini. According to Apple and Samsung, this combination should yield a max write/read speed of 1000 MB/s and 1050 MB/s. However, when I use Blackmagic's Disk Speed test app, the T7 consistently gets write speeds of about 1500 MB/s (and read speeds of about 700 MB/s, which is expected).

My question: why is the write speed consistently faster than what the connection should achieve? Does this mean that a drive like the T9 20GB might actually achieve those speeds? I thought the Mac's 3.1 Gen 2 USB-C had an upper limit of 10GB/s.

It does seem puzzling I have a T7 Shield and don't get anything close to those write speeds

(I see the expected write speeds of around 860MB/sec)

 

[CAcreeks]

Something that puzzles me, and I would appreciate knowledgeable insight: I have a Samsung T7 Shield SSD connected directly via usb-c to my M2 Mac Mini. According to Apple and Samsung, this combination should yield a max write/read speed of 1000 MB/s and 1050 MB/s. However, when I use Blackmagic's Disk Speed test app, the T7 consistently gets write speeds of about 1500 MB/s (and read speeds of about 700 MB/s, which is expected).

My question: why is the write speed consistently faster than what the connection should achieve? Does this mean that a drive like the T9 20GB might actually achieve those speeds? I thought the Mac's 3.1 Gen 2 USB-C had an upper limit of 10GB/s.

It does seem puzzling I have a T7 Shield and don't get anything close to those write speeds

It's almost as if there were two parallel write channels.

Writes faster than reads has been noted before.

https://www.reddit.com/r/macbookpro/comments/qwjbwl/blackmagic_disk_speed_test_results_for_m1_max

 

[Lettermanian]

I downloaded Amorphous Disk Mark from the Mac App Store and got these results. Now I'm more perplexed. The write speeds seem more in line with what should be expected, though I don't know why there are some very low results.







--
The grass isn't always greener, unless you shoot Velvia.

 

[Greybeard2023]

I downloaded Amorphous Disk Mark from the Mac App Store and got these results. Now I'm more perplexed. The write speeds seem more in line with what should be expected, though I don't know why there are some very low results.

Those are numbers I would expect - the random read/writes are always going to be much lower than sequential

 

[Nick on the Baltic]

You may be seeing a cacheing effect. Do you run the test for several minutes?

 

[Lettermanian]

You may be seeing a cacheing effect. Do you run the test for several minutes?

Usually I'd let it cycle four or five times, but not several minutes' worth. I can try that though. I downloaded two other speed apps and they both are giving write speeds of around 700-800 or so, which is what would be expected. Just strange that the Blackmagic app is doing this.

 

[Lettermanian]

You may be seeing a cacheing effect. Do you run the test for several minutes?

I just ran it for five minutes. Out of the many cycles it only dipped below 1400 once (to 1368). Every other cycle showed write speeds between 1400-1500, usually 1450 and above. I've tested my other external drives and they all seem to have appropriate write speeds. I'm at a loss why the Blackmagic app is reading this way when two other apps aren't.

 

[Lettermanian]

Ok, so I read the BM Disk Speed Help document, and the issue was that I had set a 1GB temporary file, not 5GB, which gives a more accurate reading. I didn't know about this at all, so I learned something new today. The new test shows write speeds between 800-900, so right where expected. Thanks for the help in figuring this out







--
The grass isn't always greener, unless you shoot Velvia.