64GB G series UHS-II SDXC wont write to specified speeds?

[funomoly]

Hi everyone - first post!

Sorry if its in the wrong section, I couldnt find a memory card area.

Q - I have a SF-G64 SDXC card which wont write anywhere close to the 299mb/s advertised speed?

I ran a Black Magic speed test (using a Sandisk UHS-II adapter) and the maximum write speed I could get after a 5GB stress test is 185.9mb/s.

Is this normal as I paid a pretty penny for two of these G series cards and have heard the M series perform pretty much the same and for half the price!

I posted a screengrab below!

Thanks in advance!

SF-G64

[Drewde]

Hi,

Can you please let me know what camera you're using. 

Thanks,

Drew

[funomoly]

its the Panasonic GH5 (with dual UHS-II slots)

[Drewde]

Thanks. Did you just run the speed test once?

[funomoly]

I think the BMST did about 8 or 9 passes (but maybe more) both on read&write at 5GB stress limit.

[IamNic]

Hi @funomoly,

does the stress test write data from the RAM (creates it on the fly) or does it write a sample file stored somewhere on the harddrive/SSD?

I am not familiar with that particular speed test.

If so I would say the reason is, that the sample file can't get read faster from the drive.

If that is not the case (the file/data get's created on the fly), I assume your USB ports cap out at the shown speeds for some reason.

Also if you use the GH5, I am curious, why you bought such overly fast cards anyways - if I am informed correctly, it records video at 400Mbit/s (4K 4:2:2 10bit) max, which is exactly 50MB/s.

- Nic

[funomoly]

Hi IamNic!

I assume the stress test is done from the RAM as it doesn't use any stored files to run off from.

Its interesting that you mention the USB port capping out at a certain speed - however both my windows (gaming) laptop and macbook have USB3 ports which I connect the card to via a Sandisk UHS-II adapter. Surely there should not be any capping if my read/write speedtest scores are consistent over both hardware systems?

[IamNic]

Hi @funomoly,

that depends on the chipset of your machines.

I have heard of transfer-speeds as low as 160MB/s on some USB 3.0 ports.

Here's an interesting article about port benchmarks: https://www.macworld.com/article/2039427/how-fast-is-usb-3-0-really-.html

- Nic

[funomoly]

Thanks for the link - interesting read!

So its the CPU / GPU combo that will determin if the card can reach its advertised read/write speeds? This does makes sense. Ill try testing on newer model and see what happens.

(Also, which stress tester do you use - could be BM giving me incorrect data speeds?)

[IamNic]

Hi @funomoly,

I use CrystalDiskMark.

Though I doubt the BM benchmark gives you wrong readings.

I hVe to ask again - why did you get such fast cards for a camera, which doesn't write faster than 50MB/s?

- Nic