Help after partitioning second drive


macrumors newbie
Original poster
Sep 24, 2016
Sheffield, UK

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?


macrumors newbie
Original poster
Sep 24, 2016
Sheffield, UK
Sorry forgot to say I tried reparing with Disk Warrior which causes a Kernel panic and the Mac reboots I need to create a bootable image and try that, Thanks DeltaMac
[doublepost=1497221373][/doublepost]Dam I need a flash drive to do that, I can unmount the entire drive as it's not holding the O.S.
[doublepost=1497222122][/doublepost]It looks like there might be two portion maps if I'm reading this right?

sudo gpt show disk2


start size index contents

0 1 PMBR

1 1 Pri GPT header

2 32 Pri GPT table

34 6

40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B

409640 3906250000 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

3906659640 262144

3906921784 3906250000 3 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

7813171784 262144

7813433928 2344012144 4 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

10157446072 262144

10157708216 781537384 5 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

10939245600 262144

10939507744 781275240 6 GPT part - 48465300-0000-11AA-AA11-00306543ECAC

11720782984 262151

11721045135 32 Sec GPT table

11721045167 1 Sec GPT header


macrumors G3
Sep 21, 2010
I'd back that up to another drive immediately, before doing anything else. You might be lucky that you can still actually access your data. I say "before you do anything else" because who knows what else you might do that ends that access.

Then, for a hopefully permanent fix, just wipe the whole drive, make your one partition, and copy the data back to it from the backup.


macrumors newbie
Original poster
Sep 24, 2016
Sheffield, UK
Wiped the entire drive no joy

I've found that if I cold boot all partitions show as expected (all empty right now) but if I restart the entire drive is missing until I cold boot again?

I texted on my old MacPro and the drive works without issue reboot or restart so not sure what the issue is but I don't think its hardware? I've tried formatting on the old machine and also PRAM reset after moving to the new machine in a different SATA bay?

Please any Ideas?
No joy tried that too same as above


macrumors newbie
Oct 22, 2014
Boot to recovery. Install reinstall OS X with out wiping drive
[doublepost=1497504125][/doublepost]Or install to the 6tb. Then migrate from old. Back up reinstall


macrumors G5
Apr 3, 2014
Hong Kong
This seems to be a common issue with larger HDD's when using an SSD as the boot drive.
Something related to timing.
May be, but I am now booting from a SSD (840 Evo), and my WD 4TB, 6TB, 8TB Red all works fine. It seems the issue is more HDD firmware related then it's capacity.
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