SSH Login Speed Issue: Armbian significant slower than DietPi on RPi4B

[1ssuc]

I've observed a significant difference in SSH login speed between DietPi and Armbian on Raspberry Pi 4B (headless setup).

 

Environment

• Raspberry Pi 4B (headless)
• DietPi (recently installed)
• Armbian (previously used)
• Both systems use default settings

 

Observations

• SSH login to DietPi is consistently faster than Armbian by a few seconds with default settings.
• Initially suspected MOTD settings, tested files under /etc/update-motd.d/. Discovered that 10-armian-header adds approximately 1 second to login time. Disabled this component but SSH login to Armbian still remained slow.
• Found related discussion on Raspberry Pi forums: SSH speed limit?
• Used the following command for testing which revealed significant speed differences:

• dd if=/dev/zero bs=1K count=1M | ssh localhost 'dd of=/dev/null'

 

and console log

 

root@DietPi:~# dd if=/dev/zero bs=1K count=1M |ssh localhost 'dd of=/dev/null'
root@localhost's password:
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 12.9425 s, 83.0 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 9.35135 s, 115 MB/s
root@DietPi:~# uname -snrvm
Linux DietPi 6.12.47+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.12.47-1+rpt1 (2025-09-16) aarch64

root@rpi4b1:~# dd if=/dev/zero bs=1K count=1M |ssh localhost 'dd of=/dev/null'
root@localhost's password:
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 29.5451 s, 36.3 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 20.0137 s, 53.7 MB/s
root@rpi4b1:~# uname -snrvm
Linux rpi4b1 6.12.19-current-bcm2711 #1 SMP PREEMPT Thu Mar 20 17:34:53 UTC 2025 aarch64

 

kernel config attachments

 

dietpi: 

 

raspberrypi-config-6.12.47+rpt-rpi-v8.zip  raspberrypi_proc_crypto.zip

 

armbian on rpi4b:

armbian-rpi-config-6.12.19-current-bcm2711.zip  armbian_rpi_proc_crypto.zip

[Werner]

I don't have a rpi4b for comparison here but 5b seems ok:

root@localhost's password: 
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 11.4733 s, 93.6 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.72436 s, 227 MB/s
root@rpi5b:~# uname -a
Linux rpi5b 6.19.0-rc1-edge-bcm2711 #1 SMP PREEMPT Tue Dec 16 21:14:01 UTC 2025 aarch64 GNU/Linux

 

[eselarm]

I get this on a Debian Trixie VM allocated only 4x Cortex-A76 on ROCK5B

1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.5407 s, 236 MB/s
2097152+0 records in
2097152+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.24198 s, 253 MB/s

Numbers are lower on RPi4B and ROCK3A.

 

However, since in-place upgrade from Bookworm to Trixie, this slow ssh login is very noticeable and also rather annoying. So this is a Debian issue as far as I can see. I had the same Debian VM running on ROCK3A and was all nice with Bookworm, although only 1GB allocated and of course is 4x Cortex-A55, so slow for crypto and compression (real-time Zstd).

 

Just after upgrade and reboot into Trixie I spent a lot of time trying to figure out why ssh login was so delayed/slow. Also noticeable that it was random, sometimes it was OK, mostly took multiple seconds. I did strace sshd and I saw just delay, waiting time in the process. More I could not figure out, would take me too much time and I had no clue where to look. The plan was anyway to move the VM (and NVME and HDD, the whole NAS setup) to ROCK5B so that is what I did then the next day or so. On the ROCK5B, I do not notice the delay that much, but it seems still to be there. I have no clue why. I use quite a lot ssh unattended, so that I don't care and notice.

 

So I basically still do not know what this is, I have not searched for It, I just see this topic and I recognise it.