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

I hooked up one of the external WD drives to an old Mac Pro running 10.11.

The drive was fine. Didn't freeze or disappear overnight for two days straight on that computer.

Does that tell us anything helpful?

I'm also about to try out a brand new Mercury drive from OWC on the iMac.

Does that tell us anything helpful?

Well, I would contact WD and ask them point blank exactly what chipset they use in your drives; then tell them that there were changes made by Apple about a year ago which resulted in problems with some Oxford chipsets. Suggest that they contact Apple to work this out; in the meantime, you'd like them to give you enclosures with different chipsets.

You had mentioned at one point that I should try unplugging only ONE of the external WD drives. Was there a reason for that? Would two of the same brand of drive cause some kind of conflict?

For a while now, I've been entering the sudo pmset standby 0 and sudo pmset autopoweroff 0 commands in Terminal on a daily basis to temporarily stop the problem from recurring (it happened again if I didn't keep inputting the commands each day). Recently, I stopped inputting them for a few days to see how the new OWC drive responded--

The problem hasn't recurred, including on the Time Machine WD, which was constantly a problem along with the other WD external drive.

In my current setup, only the Seagate external, the Time Machine WD and the new OWC drive are connected. NOT the other WD external drive. When it was Seagate/Time Machine WD/and other WD external, both the WDs malfunctioned.

Does this reveal anything? Thanks!

Funny, but I just got a new 2017 27" iMac and I am experiencing similar problems.

The Mac is running Sierra, Mac OS 10.12.5, as is yours, but mine experiences problems.

Never had this problem with my old Mac running Yosemite.

I have two Western Digital My Books; one formatted my Western Digital's utility, and the other with the Mac. Both of them become unreadable after the computer has been to sleep for some time.

I cannot eject the disks; the computer says the disks are in use. I have to re-start the Mac for the computer to fully recognize the contents of the disks.

Sometimes, the first layer of files will show; but, those folders will appear empty.

As I had said earlier, that was exactly what happened with my external disks (and they are not WD) whenever I let my Mac sleep. It was determined that the chip used in the enclosure for the externals was suddenly no longer compatible with/talking to the USB ports because Apple updated some firmware on them. So, my bet would be that it has to do with the chipset WD used - I would contact them and ask very specific questions.

Apple and WD were unable to provide a resolution to this problem. The hard drives work fine on other computers.

Maybe try unplugging one of the WD drives and see if that problem still happens, or if it's two of them somehow conflicting on the updated OS.

I bought a different drive (yes, I've wasted a lot of money dealing with this situation) and am now only using a single WD drive; I use terminal commands to prevent hibernation mode.

Apple and WD were unable to provide a resolution to this problem. The hard drives work fine on other computers

.

WD is known for their cheap enclosures (the drives are ok). They also use the Oxford chipset which was causing the non-communication problem with the updated USB ports in my case. And, the WDs may work on other computers - only a good comparison if the other computers are the same models with the same OS.

My drives were from OWC (macsales.com), but they were also using the Oxford chipset. They and the Apple engineers determined that it was the chipset which was no longer communicating with the updated firmware in the USB ports. They replaced the hard drives for me (different chipsets in the enclosures) and I haven't had a problem since.

In System Preferences, under Energy Saver, I unchecked "Put hard disks to sleep when possible".

It's only been a day; but, so far the disks have been recognized by the iMac.

Does that mean that the disks will continue to spin even when not needed? Anyone know for sure?

Western Digital also has an option in their WD Drive Utilities to put the disks to sleep after a certain interval. (The panel says that the Mac OS System may override that setting.) Anyone have any experience with this?

As for the WD utilities - I do not allow any external mfr's utilities on a hard drive; they are superfluous = not needed and, especially with WD, tend to create possible problems. So, I format any new hard drive by erasing it and then formatting it within Mac OS's disk utility. So, I cannot answer that question.

And, I've always had the "put to sleep" options checked and have not noticed a problem with it - I do uncheck that when I am doing something processor intensive such as video rendering/burning or when I'm updating or creating a new clone as I do not want to have it go to sleep inadvertently. Don't have any experience with Time Machine since I don't use it.

Is your external drive a Western Digital?

Mine are (two of them). What worked for me was removal of the WD Drive utilities from the computer disk. (Also, I installed something from Paragon, but there was still s problem. I haven't had a.problem since deleting the utilities.

I spoke to Apple senior advisor and they said that it should not have matter if it was plugged in or not.

They are wanted me to do an image capture and a video from my phone to send it to tbem

Do you remember what was the exact setting that it changed?

Kudos! This tip got my drives auto mounting again.