External drive unaccessible after sleep

I own two external Western Digital MyBook USB hard drives, which I have used with my old iMac (died recently (sigh) ) without any problem. The hard drives have been connected on separate iMac ports using USB2.0 and I have turned on WD Security.

Now I have a new Mac mini and I have migrated (with the Assistant) my old settings and everything from my old internal drive to the new Mac mini internal drive. Since the Western Digital hard drives support USB3.0, I have connected both drives to the USB3.0 ports.

Everything works fine until the mac goes into sleep mode and the drives spin down. After waking it up, the drives start to spin up but I am not longer able to view/access the content of the external drives. It seems that Finder does not wait long enough and does not reattempt to access the drives.

What I have tried:
System Control->Energy Settings: Do not deactivate hard disks
WD Utility: Deactivate Sleep Timer

Maybe MacOS has migrated old drive configurations from the old internal disk which causes the problem but I don’t know how delete those configurations.

Any suggestions

Hard drive sleep behavior settings are independent from the system (Do not go to sleep as long as the system remains active). Once the computer goes to sleep it is up to the system to awaken your hard drives. However, if the current system is unable to supply enough power to resume activity, then your units will need to be manually reconnected. There are no software settings or configuration settings able to prevent this beyond your computer’s hardware configuration.

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Actually the drive is waking up but still the computer cannot access the external drive.

In the mean time I could solve the problem- It has been related to WD Security. I have a recognized in the log an entry that the driver could not access a key which had been necessary to re-authenticate.

Now I can activate WD-Security on my new mac without any issues.

is it this your problem? After sleep mode in my Mac I can not access to the disk.
Check this video: Wd My Book

Having the same exact problem with two brand new 2 TB WD My Passport for Mac drives that I purchased in January. Those drives replaced two Seagate 1 TB USB 3.0 drives that worked fine (I was only upgrading to get more backup space.) The video David212 posted above shows exactly the symptoms I am experiencing. I have disabled both “Put hard disks to sleep when possible” (in System Preferences–>Energy Saver) and “Sleep Timer” (in WD Drive Utilities), as instructed by WD tech support, but that did not fix the problem.

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Update: WD sent me a My Passport Ultra as an RMA on one of the failing My Passport for Mac drives. Unfortunately the new drive fails even more spectacularly-- not only doesn’t it wake up when the computer wakes up, but the partition map was corrupted when that occurred. At this point, my only real choice is to throw these two drives away and purchase drives from another manufacturer. If I can’t trust that my backup drive isn’t going to eat its face when the computer wakes up from sleep, then that drive is useless.

I went back and forth with WD tech support for months. I tried everything they suggested, and nothing worked. They were quite difficult to work with, since the case would often be assigned to a new tech support representative every time I replied, and even when it wasn’t, they kept responding as if no one had read the conversation thus far. I had to keep repeating myself and answering the same questions over and over again. I finally stumbled upon this thread and was inspired to try uninstalling all WD software (including WD Utilities) from my Mac. It appears that that solved the problem. That’s a shame, because I also use a My Book Thunderbolt Velociraptor Duo, and WD Utilities is the only way to check the RAID status on the Duo.