Question USB-C slows down but only after time

[YuliApp]

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]

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

 

[YuliApp]

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]

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]

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.

 

[sdifox]

The ssd uses onboard ram as write cache. Once you exceed the buffering capacity, you get actual write rate of the NAND chip.

 

[YuliApp]

So it is writing speed limit not a reading speed limit... Interesting. And how come it is only around 80MB/s? Shouldn't even the raw writing speed be faster?

 

[sdifox]

So it is writing speed limit not a reading speed limit... Interesting. And how come it is only around 80MB/s? Shouldn't even the raw writing speed be faster?

Depends on what you bought. 80 does seem low for SSD. Maybe change the connection to enable write cache? Make sure to use eject if you do enable write cache.

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[YuliApp]

Depends on what you bought. 80 does seem low for SSD. Maybe change the connection to enable write cache? Make sure to use eject if you do enable write cache.

80 I would expect from rotating drive, not SSD.
It is internal SATA SSD software raid. I am only reading from USB.

 

[sdifox]

80 I would expect from rotating drive, not SSD.
It is internal SATA SSD software raid. I am only reading from USB.

I get 150MBps write to USB hdd. Mind you it's a Hitachi enterprise drive. But the WDs are about 130 until they are almost full.

 

[YuliApp]

I get 150MBps write to USB hdd. Mind you it's a Hitachi enterprise drive. But the WDs are about 130 until they are almost full.

yea that is what i would hope for. 3-500MB/s.

 

[Eug]

This is likely normal behaviour... unfortunately.

Also, I don't think those drives have any DRAM.

I get 150MBps write to USB hdd. Mind you it's a Hitachi enterprise drive. But the WDs are about 130 until they are almost full.

You wouldn't get that for small file writes.

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

The ssd uses onboard ram as write cache. Once you exceed the buffering capacity, you get actual write rate of the NAND chip.

DRAM on SSDs is not primarily used for write cache, but AFAIK, those drives don't have DRAM anyway.

Remember, a typical modern DRAM-endowed 2 TB SSD might have say 2 GB of DRAM cache. If the drive can write at 7 GB/s, then 2 GB DRAM used as write cache wouldn't even last 0.3 seconds for large sequential transfers, which would be pointless.

However, the same drives do have several hundred GB of cache, but it is pSLC cache, which has nothing to do with DRAM.

 

[YuliApp]

It is not a small file at all. It is 10s to 100s of GB single file. Starts transfering in 1GB/s range, then slows down and keeps at around 80MB/s. I was assuming the bottleneck was USB as I can do more over Ethernet and way more drive to drive. But it is only reading from USB. So was not sure where it comes from. It is weird.
It is same if I use TotalCommander or Explorer to copy too.

 

[Eug]

It is not a small file at all. It is 10s to 100s of GB single file. Starts transfering in 1GB/s range, then slows down and keeps at around 80MB/s. I was assuming the bottleneck was USB as I can do more over Ethernet and way more drive to drive. But it is only reading from USB. So was not sure where it comes from. It is weird.
It is same if I use TotalCommander or Explorer to copy too.

One single file that is say 100 GB? Because that is very different than say a 100 GB directory full of various sized files. Also, how much space do you have left on the drive? It sounds like you're running out of pSLC cache on a partially full drive and it's slowing way down. How long is it at 1000 MB/s?

I'm assuming it's not overheating. Does the drive feel hot, or merely warm?

 

[YuliApp]

First, thank you that you care.
Files are at least 5GB - to 200GB. It is not overheating, sits on the top case fan, not even warm for hand (it is T9 in metal case with rubber coat).
The source drive is usually 50% free (2TB total)
destination drive is 8TB software RAID with around 50-30% free
It runs usually few seconds, 10-20 above 1GB/s. Then drops and never recovers (you have to stop copying, wait some time, then it works again. immediate restart not).

I can copy TO the local drive above 100MB/s from network, well even from Internet or more from another built in drive.

 

[In2Photos]

What cable are you using? There was a thread recently where cable type and length affects USB speeds. I have a post in that thread showing my results with a Samsung T7 1TB SSD. Using the short cable that came with the drive yielded the best results using Crystal Disk Mark for the benchmarking. I didn't try copying any specific file sizes but I could try if you'd like.

Discussion - USB 3.0 / USB-C cable length versus throughput

I sold a customer a Crucial X6 external SSD which came with a USB-C to USB-C cable which was about 10-20cm long at most. Out of curiosity I did a quick throughput test on it and got about 500 megabytes/sec out of it. As the customer plans to work with the drive while sat in their armchair, I...

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[mikeymikec]

@In2Photos I would have thought that if it was cable related then the throughput should surely be ~80MB/sec throughout?

80MB/sec seems low for TLC after the cache has been used up though. I wonder if Samsung revised the specs downwards since the AT review and now it's QLC NAND or worse.

 

[In2Photos]

@In2Photos I would have thought that if it was cable related then the throughput should surely be ~80MB/sec throughout?

80MB/sec seems low for TLC after the cache has been used up though. I wonder if Samsung revised the specs downwards since the AT review and now it's QLC NAND or worse.

I agree it doesn't seem plausible that it would hit higher speeds than throttle, but perhaps since the cable is a "dumb device" the drive isn't aware of it's throughput capability so it tries to push the data through for a short duration before throttling? I have seen stranger things.

It's also possible that the OP is experiencing something like the Hynix P41 drives maybe, which so far doesn't have a explanation or fix.

 

[YuliApp]

Can't be the cable, i used two different, it is very short (like 30cm) and is the one packed with the drive. It was first thing I suspected, because my camera is very sensitive to it. But now when So far no hints, i plan to conduct a more detailed research. I really was hoping for some "duh" moment.

 

[In2Photos]

First, thank you that you care.
Files are at least 5GB - to 200GB. It is not overheating, sits on the top case fan, not even warm for hand (it is T9 in metal case with rubber coat).
The source drive is usually 50% free (2TB total)
destination drive is 8TB software RAID with around 50-30% free
It runs usually few seconds, 10-20 above 1GB/s. Then drops and never recovers (you have to stop copying, wait some time, then it works again. immediate restart not).

I can copy TO the local drive above 100MB/s from network, well even from Internet or more from another built in drive.

Wait, so you're not writing to the T7 or T9? You are reading from it and copying to the 8TB software RAID? What RAID are you using? What are those drives? Are they hybrid drives with some cache but are still spinners perhaps?

I just copied the largest file I could find, my 26GB Outlook PST file to the T7 I have and it copied around 400 MB/s for the entire time.

 

[YuliApp]

yes exactly, only reading from USB. It is software RAID in Windows (Dynamic Drive) and consists of 5 M2 and SATA SSD drives. No spinning drives.

Copying to the same drive from another SSD over network or on same PC doesn't slow it down so bad.

400/s would be more than enough for me, even though it should be faster in theory. I just not understand why it is slows so badly when In theory i made everything right designing the workstation.

 

[Tech Junky]

software RAID in Windows (Dynamic Drive)

Looks more like JBOD since the drive sizes don't match.

So, the "raid" slows down the copy process.... what happens if you do it to a single disk instead?

The cache will still play into things though because you're still writing to the PC which is using SSDs.... Once exhausted the copy will slow down, Now, you could drop each file individually and multuthread the process to speed things up if the PC chokes on one the others will still proceed, I do this with my TB drive as dropping a folder results in high 3GB/s to start off and then drops to 600MB/s after the cache fills up. If I MT the copies though I can maintain the higher speed regardless of the cache if that makes sense.

 

[In2Photos]

Wow, OK that is definitely weird. I get ~900MB/s read when copying that same 26GB file from the T7 back to my PC.

You say that it is not overheating, can you run HWINFO64 or Crystal Disk Mark to check temps while copying? Maybe the heatsink has become detached from the drive. So even though you have it on the case with a fan the drive or controller itself could be heating up but not the case itself.

The only other thing I can think of would be controller failure of the USB drives themselves. These drives behave the same way on any PC?

 

[In2Photos]

Looks more like JBOD since the drive sizes don't match.

So, the "raid" slows down the copy process.... what happens if you do it to a single disk instead?

The cache will still play into things though because you're still writing to the PC which is using SSDs.... Once exhausted the copy will slow down, Now, you could drop each file individually and multuthread the process to speed things up if the PC chokes on one the others will still proceed, I do this with my TB drive as dropping a folder results in high 3GB/s to start off and then drops to 600MB/s after the cache fills up. If I MT the copies though I can maintain the higher speed regardless of the cache if that makes sense.

Only thing is they mention that write speeds are fine across the network, so it's not the drives or the RAID slowing it down.

 

[YuliApp]

i will do more testing but the drives perform well otherwise, which is why i suspected the USB issue. i will do more research tomorrow. i was really hoping for some simple thing i missed.

the internal drives are cooled and cold. the usb drive is not on touch overheated and sits on a fan during copying. besides it performs well even on camera writing while sitting on the sun, T7 had also same issue and it is only metal case.