Hi, I need some advice please, I have a brand new drive WD 6tb Black (There is not O.S. partitions on the drive). Mac Pro, macOS Sierra (10.12.4), MacPro 2010 I attempted to remove one of the partitions and extend the other but this failed. Strangely all other petitions went grey and the only partition left mounted was the one I tried to delete. I decided I had to reboot which it appears was a mistake as after that the entire drive was missing. So I did various PRAM, SMC resets and by booting to recovery mode I was able to locate the drive and partition as I wanted..... The only weird issue is that now If I turn the Mac fully off and back on the drive appears and all data and partitions are active and accessible but if I reboot the drive disappears until I fully shutdown and restart? Not sure what this means, I have run first aid on all drives and partitions and am currently running a full drive scan using DriveGenius3 but I suspect I need an app that can scan and repair a GUID partition map Any suggestions?