Hello guys. I got a seagate 4tb external hard drive that was recognisable read/write by my iMac. At some point ( i have windows 10 installed via bootcamp ), i used it to copy some things from my windows partition to the disk, then some days later i started up my iMac ( in sierra enviroment ) and the external hard drive was not showing up ( in windows partition it shows up , read and write also ). Went back again to sierra, disk utility > First Aid, told me to Cmd+r to repair it from recovery mode, did that nothing happend. What to do ? i dont want to get in trouble to erase my hard drive, there are 2tb in there..lots of times.. Any help?!