Slow transfer/backup speeds to external USB Hard Disk (<2MB/s)


New Member
Nov 22, 2020
Hi All,

I have build an energy friendly server with Proxmox VE (6.2) as virtualisation platform for our home setup (Home Automatisation, Nextcloud etc).

Although, I am not a Linux specialist I have managed setting up everything so-far by following a lot of tutorials (both written en video).

Now, it comes to (external) backups I have reached a point where I am completely stuck and I could use some assistance.

The proxmox server has an SSD on board + 4 * 5TB Seagate hard disks which are placed in a ZFS pool. Through the GUI it is possible to make scheduled backups of the VM’s to a directory on the ZFS pool. This works fine!

However, I also want to make external backups and this is where the problem occurs.

As media for the external backups, I have purchased 2 * 8TB Seagate USB Hard disks (to change every other week). These have been repartitioned/reformatted with gdisk and formatted .ext4.

To auto mount the USB drives I have installed “pve6-usb-automount”.

When testing the backups (GUI setup) to the external hard disks I noticed that this was extreme slow. At first, I thought it was related to backup system itself.

As a test I tried coping a backup (from a small VM) from the zfs pool to the usb hard disk with rsync –progress and this shows a speed blow 2 MB/s!

To make sure nothing is wrong with the USB hard disks and the rest of the hardware I have created a system rescue - USB stick ( ) to boot from. I download a number of ISO files to test speeds with “Grsync” copying the ISO’s between the drives and the speed was > 130MB/s.

It looks like it has something to do with the setup of Proxmox VE which limits the transfer speeds to the external usb drives, but I do not have clue what is.

According to “lsusb -t” the devices are connected with 5Gb/s

I have used google a lot to find solutions, but I was not able to find a solution, yet.

Your advice/tips are appreciated!

Kind regards,


Proxmox Staff Member
Staff member
Oct 1, 2014

you can't compare rsync with a bulk copy.
If you are interested in what your USB Disk is capable use fio[1] instead.
When you backup a CT with rsync the first time you have to read/write many small (<4KB).
This is not the best pattern for speed :).



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