Unbootable MacBook Pro can't boot up through an external HD
I have a MacBookPro 2015 with High Sierra. It can't boot up. It is stuck at the startup black background with apple logo and the progress bar. In verbose mode, I saw I/O errors. I think the SSD is having problems. I want to get some files from the internal drive. I have a hard time booting into the internal drive recovery mode. I can boot into the internet receovery mode, but it takes a long time.
So I boot into the recovery mode with a thumb drive (a bootable High Sierra installation drive). However, I have problem creating disk image of the internal drive or recover the internal drive to an external drive with Disk Utility. I have tried with terminal to copy the files/directories from internal to external, but cp/mv commands do not work:-(
So I have installed Mojave MacOS on an external USB drive from a new iMac with Mojave. The external drive can boot up the iMac. But the Startup Manager in the recovery mode (through thumb drive) can't see the external drive! I unplug the thumb drive, and the thumb drive and EFI boot are unmounted. I plug the thumb drive back, and those 2 drives show up again. So I try this with the external drive, but it still can not see the external drive with Mojave. How can I boot up the MacBook Pro with my external drive?
Any suggestion is much appreciated!:-)