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Since Update 10.12.4 MMY External Hard Drive Won't Mount on Restart

After my iMac restarted with today's update my LaCie hard drive is not visible, needing to mount it manually. This never was a problem before. I restarted the Mac and the same problem. What happened, did the update change something in my External Hard drive.

iMac, macOS Sierra (10.12.4)

Posted on Mar 28, 2017 1:09 PM

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Posted on Apr 1, 2017 12:43 AM

Seems like the update chanced the default preferences to automount external drives on startup.


I found a way to fix this.


Open terminal an write this:


sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool YES

58 replies

Apr 7, 2017 3:48 PM in response to BertingAP

(Mac mini (Late 2012)) I do have same problem, My external drive (WD My passport 2TB) was connected during update to 10.12.4 and after update my drive is not showing up. I was keeping every important data on that drive and now I am frustrated what to do to get my data back, My drive is just only showing on system report, neither on disk utility nor any other Mac system as well. I don't know what this update has done to my drive ? Please help me to get my data back...!!
User uploaded file

Apr 7, 2017 3:55 PM in response to chandanankush

chandanankush wrote:


(Mac mini (Late 2012)) I do have same problem, My external drive (WD My passport 2TB) was connected during update to 10.12.4 and after update my drive is not showing up. I was keeping every important data on that drive and now I am frustrated what to do to get my data back, My drive is just only showing on system report, neither on disk utility nor any other Mac system as well. I don't know what this update has done to my drive ? Please help me to get my data back...!!
User uploaded file

Read MRCROMs statement above where he said to:


Open terminal an write this:


sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool YES


I was having a similar issue and it worked. After I entered the command I restarted the computer while also resetting the PRAM and now it seems to work fine.

May 28, 2017 4:09 PM in response to bugdoody

These are my external drives (I have both the Mercury Elite Pro size and the newer Mini version - two of each):


https://eshop.macsales.com/shop/external-storage?_ga=2.239729731.117918172.14960 12229-1347876559.1495985158


They actually had a problem with the Oxford chipset in some of them some time ago and my iMac would not wake up or actually shut down if one was attached (and the drives would stop working as well). Macsales worked with Apple whose engineers acknowledged that there was some sort of change during an OS update which made the chipsets of the external enclosures not be able to communicate properly with the iMac. OWC switched out the drives for me (they were covered by warranty) and the new ones had different chipsets in them. I do not know what chipsets WD uses and would not be able to look it up without knowing the exact model/year. Nor would I be able to guess - it is a tricky problem and of course, everyone will blame the "other guy". This is the chipset they are using now in the Pro Mini:


User uploaded file


I did find this article which shows far more specs than the WD website and does mention an Oxford chipset for some of their drives.


The only way I can think of that you could prove that it was one or the other is to have a different Mac with a different (older) OS version and test one of your drives with that. If it does the same thing, then it is not OS related (obviously).

Mar 28, 2017 2:55 PM in response to BertingAP

Have you tried to do an SMC and NVRAM reset? Neither will hurt and may help with the possibility that the USB ports are no longer communicating correctly with the chipset in the enclosure of your external harddrive.


Reset the System Management Controller (SMC) on your Mac - Apple Support


FWIW, I do firmly believe in restarting/booting up my devices at least 1 - 2 times per week; a lot of background cleanup by the OS is done during that process.

Mar 28, 2017 2:00 PM in response to BertingAP

I have a similar issue with one of my EHDs, however because I rarely restart so it's not an issue. Have you considered putting the computer to sleep when it's not being used rather than shutting it down? My Macs (iMac, Mac Mini and MacBook Air) all stay on for 20-30 days at a time with no problems, that have been operating like that for years.

Mar 28, 2017 4:26 PM in response to babowa

I did this, without any change. Since the update, my iMac is very slow to start up just sits there with black screen for more than 30 sec then the chime then it starts up as usual. The only thing missing is my external hard drive. It appears the update has messed something up, because my MacBook is fine, with the same update.

Mar 30, 2017 8:57 AM in response to mrcrom

mrcrom wrote:


I have a "WD My Book for Mac" which I´m using for Time Machine. Worked fine for years, since I updated to 10.12.4 it is not mounted automatically when I start the Mac. I can mount it manually with diskutility an then it works fine until I reboot.

I have the same issue, the solution (I know it's not what you want to hear) is to not reboot so often. When your iMac is not being used, put it to sleep. That should take care of your problem. I've been doing this for 10+ years and have had zero problems, Macs do not need to be shut down at the end of every day.

Mar 30, 2017 9:10 AM in response to mrcrom

Was that drive plugged in while updating? I always unmount/unplug any external peripherals except keyboard and mouse before updating/upgrading OS.


Other than that, the only other cause I can think of is that the update changed something in the USB ports which makes it more difficult to discern some chipsets in external enclosures - that was a problem I had a year ago with some OWC drives and was a known problem to both OWC and Apple engineers at the time. They gave me new hard drives (with different chipsets) and I haven't had a problem since.

Since Update 10.12.4 MMY External Hard Drive Won't Mount on Restart

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