Do All USB Hubs Slow Copy Speed?
April 1, 2019 9:22 AM Subscribe
I use a decent quality 4-plug powered USB hub. My USB 3 external drives get only half the read/write speed through the hub that they get if plugged directly into my computer (even if I'm not doing simultaneous tasks with the other drives), according to AJA System Test. Are there hubs that don't sacrifice performance?
I have a 4-port HooToo USB 3.0 hub and I have never noticed a reduction in speed when using it compared to when plugging into a computer directly. I haven't run any tests to check if there is a difference though.
posted by any portmanteau in a storm at 10:10 AM on April 1, 2019
posted by any portmanteau in a storm at 10:10 AM on April 1, 2019
Response by poster: Sunburnt, definitely a 3.0 hub
posted by Quisp Lover at 10:16 AM on April 1, 2019
posted by Quisp Lover at 10:16 AM on April 1, 2019
My understanding is that all devices attached to a hub are sharing throughput speeds to the maximum speed of whatever port the hub is attached to - it's not necessarily splitting the speed in half, but probably has added processing costs as well.
When you refer to drives in the plural, are you trying to write to multiple drives at once? Or are we talking single read/write operations to one drive at a time?
posted by aspersioncast at 12:36 PM on April 1, 2019
When you refer to drives in the plural, are you trying to write to multiple drives at once? Or are we talking single read/write operations to one drive at a time?
posted by aspersioncast at 12:36 PM on April 1, 2019
Response by poster: aspersioncast,
As I said:
even if I'm not doing simultaneous tasks with the other drives
posted by Quisp Lover at 12:47 PM on April 1, 2019
As I said:
even if I'm not doing simultaneous tasks with the other drives
posted by Quisp Lover at 12:47 PM on April 1, 2019
USB 2.0 hub chips have a transaction translator that interfaces between the 2.0 speeds upstream and slower 1.1 speeds downstream.
I'm not aware of any USB 3.0 hub chips that support transaction translation. This means that if you have any lower speed devices connected to your hub, the upstream speed will be limited to the lower speed for those transactions. It will switch between super speed and hi speed and full speed for each device's transactions.
What this means is that if you have lower speed devices connected to your hub, like a mouse or keyboard, it will eat into the bandwidth of your super speed device. Even if you are not actively accessing those other devices, there is typically some periodic background polling going on.
The other issue is whether your USB hub is self-powered or bus powered. If bus powered, meaning no external power supply, your disk device may be limiting its performance in order to reduce its power demand from the hub. You might find you get better performance with a self-powered hub.
posted by JackFlash at 1:12 PM on April 1, 2019
I'm not aware of any USB 3.0 hub chips that support transaction translation. This means that if you have any lower speed devices connected to your hub, the upstream speed will be limited to the lower speed for those transactions. It will switch between super speed and hi speed and full speed for each device's transactions.
What this means is that if you have lower speed devices connected to your hub, like a mouse or keyboard, it will eat into the bandwidth of your super speed device. Even if you are not actively accessing those other devices, there is typically some periodic background polling going on.
The other issue is whether your USB hub is self-powered or bus powered. If bus powered, meaning no external power supply, your disk device may be limiting its performance in order to reduce its power demand from the hub. You might find you get better performance with a self-powered hub.
posted by JackFlash at 1:12 PM on April 1, 2019
Response by poster: Devices connected to hub are all USB 3.0. external drives.
posted by Quisp Lover at 1:15 PM on April 1, 2019
posted by Quisp Lover at 1:15 PM on April 1, 2019
Ah, missed that, when you said copy speed I assumed you were copying from one of those drives to the other.
I would suspect the hub then.
Try doing a system test from the terminal just to see if AJA is accurate:
https://medium.com/@kenichishibata/test-i-o-performance-of-linux-using-dd-a5074f1de9ce
posted by aspersioncast at 1:34 PM on April 1, 2019
I would suspect the hub then.
Try doing a system test from the terminal just to see if AJA is accurate:
https://medium.com/@kenichishibata/test-i-o-performance-of-linux-using-dd-a5074f1de9ce
posted by aspersioncast at 1:34 PM on April 1, 2019
This thread is closed to new comments.
posted by Sunburnt at 9:33 AM on April 1, 2019 [1 favorite]