Yosemite ejects external drives

Well, add me to the list. Same problem, nothing works, no idea what to do now. I've just submitted the following online feedback to Apple, FWIW:

"Since upgrading my MacBook Pro to Yosemite (10.3.3) last week, I have consistently received a "disk not ejected properly" error message for my external hard drive (used for Time Machine backups and other file storage) whenever I put the computer to sleep by closing the cover. I never had this problem before the OS upgrade (from Mountain Lion). I have tried all of the work-arounds suggested in the user forums (ignoring the drive in Spotlight by adding it to the Privacy list, changing the energy saver sleep settings in System Preferences), but nothing helps. Whenever I reopen my laptop after closing the cover, I get this error message and the external disk icon disappears from my desktop. The external drive is a LaCie Little Big Disk 5400 2TB external drive purchased 2012."

I appreciate all of the efforts and advice of others on this thread. Just wish that Apple would acknowledge and fix the problem!

Add me to the list. My external drive had worked fine until updating to 10.10.3.

Now when waking from sleep I see the infamous, "Disk ejected improperly" message.

Another thing I've noticed, when working on my iMac throughout the day, I hear the drive powering up as if it had gone to sleep. It had never done this before. I have "put hard drives to sleep" unchecked in Energy Saver.

Something is messed up and I'm attributing it to Yosemite, not the drive.

Hey Apple, are you listening? Any suggestions? Any explanation? Any anything?

I can offer this update to my situation: I have an external lightening drive that is also randomly being ejected at night. The drive is set to never go to sleep. I have tried it plug directly into my iMac as well as into a USB hub. The ejections appear to be random. It does it 2 or 3 times a week in a 5 day period. It doesn't matter whether I've use the computer the night before or not. It doesn't matter whether I have saved to the drive or accessed the drive hours beforehand or not for several days. There seems to be no consistency to why the ejections occur and it's something I've only experienced since transitioning to Yosemite. But, I can say I have a second older external firewire drive that has not once experience any ejections at all.

I am going to throw my name in the ring on this. I have the same problem with my LaCie external drive. I'll try the workaround when I can get my Mac to see it again. I'll follow the post in hopes a solution is found.

An SMC reset worked for me, at least for now. I can now close my MacBook Pro cover to sleep the computer without a bad eject of my LaCie external Thunderbolt drive, although the reset does seem to have slowed down my whole system for some reason.

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

I don't know why some workarounds succeed and others fail, with different experiences for different people, but I guess the lesson (for now, at least, until Apple manages to fix the OS X bug) is to try them all.

Same. I've got 4 external drives attached to top my late 2013 MacPro in a Mediasonic ProBox HF2-SU3S2 4x Bay 3.5" Hard Drive Enclosure. One of those drives is my TimeMachine. Since going to 10.10.3 every morning when I wake my monitor I've got 4 improperly ejected disk errors but the drives have re-mounted themselves. The only thing I've got checked in Energy Saver is "prevent computer from sleeping automatically when display is off" and this is my most recent setting attempt. I've run through most of the other possible solutions in this thread. We'll see in the morning.

It's very unsettling because last year I had a major failure in my old tower where my drive became corrupted and this corruption was apparently copied to my TImeMachine. Lost A LOT of stuff due to lack of backup redundancy, but that's another story. I've had more problems with Apple hardware and software in the last 2 years combined than in the previous 30! I sincerely hope this isn't the future of the company.

I don't think it's just happening with drives... I think it's the actual connections to the machines.

I'm using a thunderbolt 2 dock, with a second screen connected to it. That would randomly just shut off... turn on... sometimes repeat a few times until it was "good".

To the other thunderbolt port on my iMac, I have a Lacie 8TB for backups. That also disconnects randomly - but in this case, instead of powering back up like the dock

I have the same issue with my new imac Retina 5K, which came with Yosemite installed. It keeps ejecting my two brand new Seagate 2TB slim drives.

I get the dreaded Disk Not Properly Ejected after imac wakes up from sleep. I spent hours on the phone, tried all combos of Power setting, reset SMC, PRAM, Reload OS, tried it with new User added, used a new partition on the internal drive with clean OS install, turned off Spotlight for external disk, and did pulling the network cable etc. Apple tech directed me to the Genius Bar where they replaced my logic board on my 3 months old imac. All above did not solve the problem. I tied the two Segate 2YB drives with macmini (2009) with Yosemite and an older imac (2010) Maverick, they work OK. Since the older macs are equipped with USB 2.0 and the new imac is equipped with USB 3.0. I contacted Seagate and was referred to the thread about "Disk not ejected properly" they blame Apple. My suspicion it is an issue related to USB 3.0. I moved the two Seagate drives to an externally powered UBS 3.0 hub and have not seem the problem since. I wish Apple Engineers find a solution to this problem.

I don't think this issue is related to one specific type of connection. My Seagate external is hooked up via FW800. I see that others here are using Thunderbolt and USB 3.

Agree. My enclosure is USB 3.0 HOWEVER everything had been running fine for the 8 months or so I've had this new MacPro. Problems began around the time of my upgrade to 10.10.3. I definitely think it's software.

I have just hooked my drives up to an OWC Thunderbolt 2 Dock, we will see if the problem is solved and get back to you

It's out of control now today... 5 times in the past hour in the middle of a studio session. Class action anybody?

II've had crazy days where it happens constantly and then I go weeks without having it. I'm in the middle of such a streak right now. I have no idea why it's not doing it but it's stopped.........for now.

"Thank you" to many of you. Some ideas worked -- for a while -- and then bombed out. The only thing that has worked lastingly for me on my 5-year old iMac with Yosemite 10.10.3 is to get into System Preferences / Energy Saver and set "computer sleep" to "Never". This has been the only solution for me with an outrigger Time Machine hard drive on a USB port. C'mon APPLE ! What is taking you so long to clue us in? . . . . . . . . or don't you know ?

Setting the CPU never to sleep has worked for me too as well as plugging my Seagate 2TB slim drive into a powered USB 3.0 hub instead of a direct connection to the imac. But these are work around. Apple needs to have a fix for this major issue that affects so many.