Hi, yesterday I bought a new 8tb WD external hard drive, it came formatted as exFat, I tried to format it to HFS but after a few seconds it failed and I got the message drive failed to unmount, then the driver dissapeared, Disk Utility would display it as disk5s1 but every attempt at formatting the disk would fail, took it to a pc and formatted again but my iMac wound;t see it, even the experts at apple place couldn't format it and I was told to try and get a new one, in desperation I took it to a friend who owns a 2007 mac mini , as soon as I plugged the drive it offered to initialise it, and I was able to use it, I thought this a bit odd and tried two old drives formatted as ms-dos and the same thing thing again, and I'm sure it is High Sierra because I did installed Parallels and Windows 10, which sees and formats the drives but back to High Sierra the drives disappear even after a few re-boots, is there something am I missing?