USB drive is slow - a tale of two setups

[Redbecca]

I have two machines running Debian, with USB 3 4tb WD Passport drives attached. One of them the performance is inconsistent and very slow. Both machines have an OS drive, I am using the USB disk to backup documents to each of them.

Server Black
Debian GNU/Linux 9.2 (stretch)
i5 processor, USB 3 port
16gb RAM

Server Silver
Debian GNU/Linux 9.2 (stretch)
i5 processor, USB 3 port
16gb RAM


The problem is Server Black has very inconsistent performance when accessing the USB drive but both report they are plugged into USB 3 ports.

Here are the results of a few of these:

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dd if=/dev/zero of=/data/testfile bs=1G count=1 oflag=direct

Server Black
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 34.342 s, 31.3 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 38.5034 s, 27.9 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 54.9556 s, 19.5 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 38.9084 s, 27.6 MB/s


Server Silver
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 12.3527 s, 86.9 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.7403 s, 91.5 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.247 s, 95.5 MB/s
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.5433 s, 93.0 MB/s


I spent a couple days testing these things. My suspicion was Server Black was not really plugged into a USB 3 port.

Server Black
Bus 004 Device 002: ID 1058:25e2 Western Digital Technologies, Inc.
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub


Server Silver
Bus 003 Device 002: ID 1058:25e2 Western Digital Technologies, Inc.
Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

What could be causing the performance to vary between two pieces of hardware that are supposed to be the same?

[4D696B65]

BIOS settings are same?
BIOS version is same?

[bw123]

set for lower dma than capable? I think even a usb disk will use this?

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# dmesg | grep UDMA

if this is going on you will see stuff like this in /var/log/syslog or messages

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localhost kernel: [410026.367844] ata1.00: configured for UDMA/133
localhost kernel: [410026.379393] ata1: EH complete
localhost kernel: [410026.488706] ata1.00: limiting speed to UDMA/100:PIO4
localhost kernel: [410026.488756] ata1: hard resetting link