Thankyou for help. Manual partitioning did help me to install devuan properly. I think automatic partitioning is messed up for some hardware on devuan. Thank your everyone who helped me through this !

Yes guided partitioning
500 gb hdd and erasing it completely
On single os, no dual boot
It's devuan issue cause i do same steps on debian without single issue.
I tried expert install and it too shows both sda and sdb on the partitioning page and there is no way to deselect sdb (installation usb)

Installation steps

Please open above link and see the image after point no. 11.It only shows sda but in my pc it shows sda (hdd) and sdb (installation usb). Even though i only select sda.

I think it selects as well as make new partitions on my installation media usb. That's why I get an error soon after i proceed with the partitioning. I don't remember the error but it starts with something like partitions(s) dev/sdb ......