Slow USB3 data transfer speed on debian with proxmox

Issue

Recently I saw a debian proxmox system, which had a usb3 hdd mounted. The hdd write speed should have been ~100MB/s and the USB 3 connection speed was 5GB/s. However the datatransfer speed was very slow, about 5-6 kB/s. The hdd was mounted to /mnt/usbhdd01/. A short speedcheck showed the issue:

root@proxmox1:~#
root@proxmox1:~# dd if=/dev/zero of=/mnt/usbhdd01/test03012021-2036uhr.img bs=1024 count=10000
^C220+0 records in
220+0 records out
225280 bytes (225 kB, 220 KiB) copied, 35.8676 s, 6.3 kB/s 😕
root@proxmox1:~#

Solution

After some troubleshooting I found out why: /etc/fstab had the options auto,nofail,sync,users,rw:

# <file system> <mount point> <type> <options> <dump> <pass>
/dev/pve/root / ext4 errors=remount-ro 0 1
UUID=1234-4567 /boot/efi vfat defaults 0 1
/dev/pve/swap none swap sw 0 0
proc /proc proc defaults 0 0
UUID=aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee /mnt/usbhdd01 ext4 auto,nofail,sync,users,rw 0 0

After changing that to defaults and re-mounting it, speed was fast again:

# <file system> <mount point> <type> <options> <dump> <pass>
/dev/pve/root / ext4 errors=remount-ro 0 1
UUID=1234-4567 /boot/efi vfat defaults 0 1
/dev/pve/swap none swap sw 0 0
proc /proc proc defaults 0 0
UUID=aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee /mnt/usbhdd01 ext4 defaults 0 0

Short speedtest:

root@proxmox1:~# dd if=/dev/zero of=/mnt/usbhdd01/test03012021-2110uhr.img bs=1024 count=2000000
2000000+0 records in
2000000+0 records out
2048000000 bytes (2.0 GB, 1.9 GiB) copied, 20.3455 s, 101 MB/s 😊