The stock Samba was over-optimized, causing data corruption under certain circumstances. (https://bugzilla.samba.org/show_bug.cgi?id=10584). As this will not be the case in OpenWrt Samba, 70MB/sec is unrealistic.
But 10MB/sec is slow. Have you looked at the CPU usage during speed test?
Your iperf measurements would suggest that your device in its current state taps out just saturating the link long before you come anywhere close to your expected 70 MB/s of SMB throughput. Also what I find odd is that aftermarket binary named "udpspeeder", which is clearly intended to influence networking on some level, and judging from your UDP iperf results very heavily so. I would probably take the device back to pure stock OpenWrt and see if it makes any difference.
I am aware that I do not get full gigabit speed with this crappy NAS. But 60-70 Mbit/s has I when copying with the original Medion firmware always. But this supports only SMB v1.
My problem is that I can't get the iperf speed with samba (44MB/s).
iperf was recorded with a pure openWRT. udpspeeder was only on it for a short time for testing purposes, but it did not make any difference.
Does anyone know anything about Samba compression?
Your dd copy was not 5mbit/s, but 5MByte/s. That is a factor 8 in difference, assuming you didn't mean millibit.
The dd copy wasn't applied well. This way it wrote a sequence of 512 bytes. which doesn't fit well with 4k sectors/clusters.
Better use bigger blocks:
No, not twice. /dev/zero is not the harddisk, it's a pseudo device.
Are you sure the stock firmware did 70MB/sec, and not 70Mbit/sec? The network interface nor the disk can handle that speed in OpenWrt, and Samba is CPU limited at 15MB/sec.
Encryption is expensive. So as long as the CPU is the bottleneck, avoid encrytion.
It's a potato by todays standards, Samba 4.x is a more intensive and can pretty much satuerate gbit links on hardware that isn't ancient. ARMv6 is considered "dead" since several years and people have moved on. You might get better performance using the kernel module but the hardware is very old and have quirks that don't help performance. It's a classic case of can't fix.
I have now installed Debian. Out of the box 1.5x speed read/write. So there is still something to get out. I'll continue testing.
Which possibilities besides Samba do I have to transfer data to Win11? FTP is not so smoothly integrated in Windows.
Let's see what works with NFS. And if I can find a decent NFS driver for Windows.