USB Speed Drops Off a Cliff

Mr. Macintosh · 10-24-2019, 12:28 PM

I'm running Xubuntu 18.04 on a Dell Optiplex 3020. I'm having a strange issue where the USB 3.0 transfer speed starts out around the maximum speed of my hard drive (~100 MB/s) and slowly drops off. It runs at ~100 MB/s for about 30 seconds, drops to ~40 MB/S and then drops to ~22 MB/S But I'm also having this issue with USB 2.0 as well, except the starting transfer speed is around 60 MB/S. Is there a solution to this? Or is it just a weird bug of my hardware or the distro?

uteck · 10-24-2019, 01:18 PM

I think that is normal for USB, it has a high starting speed but then tappers off, especially if multiple things try to access it.
That is part of the reason I used eSATA on my external RAID box. It was slower then USB3 top speed, but that top speed could not be maintained for large files so eSATA was constant speed.

syg00 · 10-24-2019, 05:39 PM

This is a common complaint.What I/O scheduler are you using - use this for the appropriate device

Code:

cat /sys/block/sd?/queue/scheduler

If cfq, a quick test might be to change to deadline - simply echo to the same file. This will allow the write-back throttling relief code to kick in.
I would be interested to hear if it helps.

ondoho · 10-25-2019, 03:18 AM

Quote:

Originally Posted by syg00

I would be interested to hear if it helps.

Yeah. me too.
And if it does, how to make that default for USB drives.

rnturn · 10-26-2019, 02:40 PM

Quote:

Originally Posted by ondoho

And if it does, how to make that default for USB drives.

All of the block devices (m'board-connected SATA as well as USB) on my system report:

Code:

$ cat /sys/block/sdN/queue/scheduler
noop [deadline] cfq

Which I interpret as using the "deadline" scheduler.

My Grub boot command line includes:

Code:

elevator=deadline

No ill affects (so far) from having it set this way for all drives.

HTH...

ondoho · 10-27-2019, 05:14 AM

Quote:

Originally Posted by rnturn

HTH...

Does it help with the speed?

I'm not OP btw.