Question USB-C slows down but only after time

YuliApp · Sunday at 6:22 PM

Hi there,
I have a question I am really flipping over and have not find a solution yet.
I have USB external SSD T7 and T9, both exhibiting the issue.

Copying starts fast, 1GB/s, then drops with the time to 80ish MB/s and keeps the pace.

Different cable, rotating connectors, same effect. The delay how quick it goes down is random.
Copied is on good SSD internal drive, PC specs are good too.

Is it something normal, what speed you maintain consistently?

TIA

Tech Junky · Sunday at 7:10 PM

It's the dram being exhausted and thus slowing down.

YuliApp · Sunday at 7:33 PM

really? Which DRAM, my PC has 64GB of main memory (by far not fully used) or you mean cache on the HDD or USB controller/DMA?

Tech Junky · Sunday at 8:41 PM

Dram on the portable drive or any SSD for that matter. It's how you get the insane speed for small bursts of data. When you move large chunks the dram doesn't flush and you get slower speeds.

For instance my sn770 doesn't have dram and uses the system ram instead. Single thread performance is alright but if I break it into chunks it goes faster.

YuliApp · Sunday at 8:54 PM

yes but i get insane speed even for large data, just only on the beginning. So where is the bottleneck? From Flash to DRAM, DRAM to USB or on PC side USB to DMA?
Ahhhhhhh..... Or you mean it reads instantly from flash to DRAM in parallel, then has to wait to clean DRAM to read again in paralell because it is not FIFO deal, just some "block copy" and cannot operate on half empty DRAM.

Question USB-C slows down but only after time

YuliApp

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Tech Junky

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YuliApp

Senior member

Tech Junky

Diamond Member

YuliApp

Senior member

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