Dear sirs. What’s the best OS Media for OpenWRT, SD card or CF card w/ ECC Controller, or SSD?
Sorry im a little tired. Thank you.
Is there a question here?
EDIT: looks like you have updated your post with a question...
OpenWrt will run on generally any media that is supported by your hardware. The choice of which media you want to use depends on the hardware you are using, how much space you need, and what you will be doing with OpenWrt. If it is acting as a router (most normal configurations) any media is fine. If you are using it as a NAS or other file-intensive service (especially with lots of file writing), you'll want a spinning platter HD or SSD (which are designed for a lot of writes) and those are also generally faster media for read/write operations.
I use an extroot configuration with an SD card on my VPN endpoints at home, and my travel router uses a USB stick with extroot.
Thank you! Why aren’t settings saved in a startup script?
Thank you!
what is the usecase? Router? Nas? What packages or services you use on the device?
For a networking device with no special packages, anything is OK.
If you install packages that need to write a lot to disk, you want a hard drive or a SSD
Settings are saved in UCI configuration system. https://openwrt.org/docs/guide-user/base-system/uci
Luci web interface is writing the settings in UCI as well
I’m planning on using it as a wireless access point altogether.
Thank you.
Then anything is OK, OpenWrt does not write anything to disk if it's working as wifi access point. Only moments when it writes something will be when you save the configuration or update the firmware.
If the OS is in constant rw mode. Will that open up for more data corruption on the disk?
Thank you?
not necessarily more, but perhaps bigger risk of ...
Thank you sir. How do we work around it?
UPS the device, or keep it switch off ?
rw mode means that OS can write. IF it wants to write.
OpenWrt in a router/AP setup does not write anything to disk during normal operation. It writes only when you save the config, and when you upgrade the firmware.
No writes means no risk of corruption.
Is it possible to make the OS ro and the rw when it needs to write and then back to ro again ?
Thank you 
Why ?
As bobafetthotmail wrote, it doesn't write unless it needs to, and if it crashes when there's no write activity, there's no risk for corruption.
Changing ro->rw->ro wouldn't help a thing, if it crashes during write, the same risk/chance of corruption apply.
No.
That does nothing. Corruption happens when the system is writing and crashes, which would happen anyway even with your RO/RW switching
OpenWrt is not Ubuntu. On Ubuntu you can switch to read-only mode because that is the only way to actually stop multiple services designed for a Server/Desktop from writing everywhere. But even on Ubuntu if the system crashes when writing you have problems (and if the system crashes while not writing everything is fine).
On OpenWrt nothing is writing and the system is tiny. Unless you install an application that obviously writes (file sharing, for example), nothing is writing.
OpenWrt is designed to run on the flash memory of router devices so all packages are designed to not write to root partition. This flash memory has very low write endurance. You cannot write many times like in a SSD, it will wear out and fail.
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Thank you. Sir.