Comment by ridgered4 | Hacker News Reader

Comment by ridgered4 | Hacker News Reader

> if you have a USB 3 hub plugged into a USB 3 port, multiple USB 2 devices plugged into it still cannot break through the USB 2 uplink limit of 480 MBps.

I had a weird project where I ran into this. Or rather, I was actually aware of it and tried to work around it. I wanted to attach a large number of optical drives with sata to USB converters to a single port, basically a hot attachable ripping tower kind of thing. To assure a single port would provide enough bandwidth I needed USB 3.0 throughout. But SATA to USB 3.0 converters that exist seem to have...shaky support for optical drives as they're only really meant for SSDs/HDDs. My project ended in at least temporarily failure due to that unreliability.

I remember reading about this device and not finding it a reasonable solution. In addition to not being easily available, I'd need one device per port to break the uplink limit. That wouldn't save me any money and it would be a cabling nightmare. If the chips were a reasonable price and easily available I might have looked into it more seriously anyway though.

> USB 2 uplink limit of 480 MBps.

That should be "Mbps", usb 2.0 max is 60 megabytes per second. Odd that even hackaday gets this wrong from time to time.

> Odd that even hackaday gets this wrong from time to time.

Is it? Isn't 'hackaday' just various unvetted user contributions?

I haven't frequented them in a while, but it used to be a mix of guest articles and articles written by staff, commonly about user submitted stuff.

Oh ok, you're probably right (I've ended up there occasionally e.g. via HN but never frequented) I just misunderstood.

There's a bunch of weirdness. Lack of USB2 to USB3 translation is one of them, but there's also a lack of USB3 and USB2 concurrency.

E.g., if I put a USB 2 device on a bus with a USB 3 flash drive I would find constant stalling due to the USB2 bus activity. It even went so far that the output of `lsusb -t` would show the speed downgraded to 480Mbps at the bus level and not just the port. This has since been changed, but I notice stalling and bad performance. This is supposed to be fixed in USB3.1 and 3.2 but I am not sure we're going to see it in practice. The original spec does not say they are supposed to happen at the same time but the spec authors have made themselves clear that they were supposed to operate concurrently.

My pet peeve are webcams. You can only plug in a few before you run out of bandwidth.

Maybe you'd have more chance using USB 3 drives directly, unless you actually require a 3.5 inches form-factor? Another option might be to use IDE drives...

I'm using optical drives in case, so 5.25". But yes, I believe I'm going to end up removing USB from the equation entirely and just go straight SATA connection, possibly with a port multiplier solution.

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