server to server transfer with xargs and rsync fails

Hello,

I have decided to use rsnapshot to have incremental backups to another backup server. I have rsnapshot working, but the transfer speed is very slow and will take about 2+ weeks to transfer the 22 TB of data. I searched around and found a stack overflow answer on how to quickly use multiple rsync streams to speed up the process:

https://stackoverflow.com/questions/45122323/rsync-command-is-giving-error-no-such-file-or-directory-2

However, when I try to replicate the commands, it breaks immediately.

root@main_server:~# ls /mnt/user/ | xargs -n1 -P4 -I% rsync -Pa % [email protected]:/mnt/user/Primary_unRAID_Backup/daily.0/main_server/mnt/user/
sending incremental file list
sending incremental file list
sending incremental file list
rsync: [sender] change_dir "/root/Backup" failed: No such file or directory (2)
rsync: [sender] change_dir "/root/Camera" failed: No such file or directory (2)
rsync: [sender] change_dir "/root/CacheOnly" failed: No such file or directory (2)
sending incremental file list
rsync: [sender] change_dir "/root/Documents" failed: No such file or directory (2)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
sending incremental file list
sending incremental file list
sending incremental file list
sending incremental file list
rsync: [sender] change_dir "/root/Downloads" failed: No such file or directory (2)
rsync: [sender] change_dir "/root/Handbrake" failed: No such file or directory (2)
rsync: [sender] change_dir "/root/Food" failed: No such file or directory (2)
rsync: [sender] change_dir "/root/Games" failed: No such file or directory (2)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
xargs: unmatched single quote; by default quotes are special to xargs unless you use the -0 option
sending incremental file list
rsync: [sender] change_dir "/root/ISOs" failed: No such file or directory (2)
sending incremental file list
rsync: [sender] change_dir "/root/Linux_Home" failed: No such file or directory (2)
sending incremental file list
rsync: [sender] change_dir "/root/Media" failed: No such file or directory (2)
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1330) [sender=3.2.3]
root@main_server:~#

Any idea on what I'm doing wrong? I want to run this once, and then use rsnapshot going forward.