Question Could someone explain these low read/write speeds from my new external SSD ?

[infinitedrive06]

I will try to post the info as detailed as possible.

Started around 350MB/s which I thought was low to begin with and then almost halfway through shot down to 30MB/s and has been sitting there.
I did my research before buying and I know its a QLC SSD, but after this write, I will only be using it to copy to other computers.
I knew I wouldn't hit top speeds writing to the drive but I didn't think it would be writing slower than my USB flash drives...


Copying 575GB FROM MY PC: Crucial P3 1TB 3D NAND Flash PCIe Gen 3 x4 NVMe M.2 Internal SSD Read Speed: Up to 3,500MBps / Write Speed: Up to 3,000MBps

FROM PORT: USB 3.1 Gen 1 (up to 5Gbps) USB-C Port in motherboard in back of computer

WITH CABLE: Type-C to Type-C USB cable (10Gb/s)

TO: Crucial X8 External SSD USB 3.2 (Gen 2 Type-C) Read Speed Up to 1,050MBps / Write Speed Up to 1,000MBps

Edit: Now I'm copying the same 575GB from that External drive to a laptop and getting similar results.
Laptop has a Thunderbolt 3 port and it's copying to a 1TB Sata SSD with a 500MB/s read / 450MB/s write spec.
Was around 500MB/s for about 60% of the way and then dropped down to around 5-7MB/s that occasionally will jump up to 175ish for a few seconds and then back down.


Thanks in advance.

 

[Eximo]

Once you fill up the SLC cache on a QLC drive, it is going to have to go back and re-copy data to fill the cells completely. 4-bits per cell should mean that once you hit 200GB or so (assuming an empty drive), the drive is going to have to start cleaning itself up and re-arranging all the data on the drive.

 

[infinitedrive06]

Once you fill up the SLC cache on a QLC drive, it is going to have to go back and re-copy data to fill the cells completely. 4-bits per cell should mean that once you hit 200GB or so (assuming an empty drive), the drive is going to have to start cleaning itself up and re-arranging all the data on the drive.

My PC also has 2 teal USB-A Ports (USB 3.1 Gen 2 [up to 10Gbps]) - I was made to believe I would have better speed transfers with the USB-C - USB-C cable, but would the speeds be better if I put the adapter on and plugged into the teal USB-A?

 

[Eximo]

Shouldn't make a difference. It isn't the USB connection holding you back, but the drive's design.

QLC is great for write once, read many. Ideal for game and multimedia storage. But not so great at handling large amounts of writes at once.

Drive is basically sitting there constantly running trim while you are telling it to consume more data. A lot of QLC drives don't have DRAM cache either.

The "Up To" speeds are correct. If you take a small contiguous file it will write 1 bit per cell and move on to the next going very fast. Soon as all cells on the drive have at least one 1 bit written, it has to take 4 bits from four cells and consolidate them to a single 4-bit cell. (Kind of like running a compressed drive)

 

[infinitedrive06]

QLC is great for write once, read many.

Like I mentioned, that is why I bought this drive. It will only be used to copy that same 575GB to other PCs. I was originally surprised that the initial "write once" was so slow but I figured it didn't matter much until it was also slow writing from the Drive to the laptop.

 

[Eximo]

TLC drives behave the same way. If the target SSD is pretty full, you are going to run into the same problem.