Q: Yosemite ejects external drives

I just read a technical article that stated "put hard drive to sleep" no longer impacts external drives.  I see on mine that it makes no difference if checked or not.  In may case my external drive enclosure has a built in power saving feature anyway so no big issue.  I found it is best for my use to keep the drive spinning as TM will wake it up every hour anyway and it only causes wakeups resource spin error messages in the console if it constantly spins up which happens quite often when I open an app. for some reason.

Spot on!  I recently upgraded to Yosemite and my external hard drives have been ejected for the past week.  I followed your tip by disabling "Put hard disks to sleep when possible" in 'System Preferences'>'Energy Saver'.  Hey presto, my external drives have stayed on line.  Thanks!

having same problem with LaCie 2Big thunderbolt2 hard drive randomly dismounting from Mac Pro late 2013 running 10.10.2. talked with Lacie and they even sent me a new hard drive but it still dismounts. This happens not only when cpu goes to sleep. Have tried all above suggestions including disabling spotlight, not using power saver. new cords,etc. spent 2 hours with Apple support last night and their final suggestion was to have apple store run hardware diagnostics on CPU, but since I have another thunderbolt ext drive that has no issues they feel it is a problem with this type of LaCie external drive. Looking into Pegasus drives now.

Drat. One week after trying the Spotlight workaround, I woke up the computer to get the "disk not ejected properly" error on my Time Machine drive. It's a lot better than it was (where it used to happen at least once a day), but certainly not "fixed."

The Apple support expert also advised me to go to the Apple Store and see the repair guy for hardware diagnostics.  That was after 5 hours (in one day, more hours on two other days) of trying everything, wiping the computer and reinstalling the OS (twice), partitioning the computer HD etc.

The next day, I decided to really dig into the forums and found one "fix" that worked for me (so far).  I not only removed the external HDs from the Spotlight search (in privacy tab) I also unchecked all the choices for Spotlight.  Basically, I have no Spotlight now, I don't like that, but at least I can run all of my external HDs, which mostly are Western Digital My Passport.

I also updated the firmware of the externals and turned off the "go to sleep" mode in the utilities. 

Wow thanks to you all, once again to power of the many !! I use alot of macs at work...lots of them...and also hak-intosh... i add this nasty bug on hack-intosh hardware and was mostly sure it was related to my unsupported hardware ....until i looked here and found the spotlight solution... it worked...  all my external drive were exFAT MBR maybe this info might help.

i updated to yosemite, and tried disabling spotlight and disabling put hard disks to sleep, and still getting the eject error message. this time, i was working on my machine, and got the same message while everything was active. everything worked perfectly the day before updating. thoughts?

After my iMac being happy for a while, it now has started ejecting disks again when it goes to sleep.

I was called by a helpfulApple person some time ago, now to call him back.

I have the same problem. iMac 5k one month life, i have problem with only my new 2tb usb3 seagate backup plus, instead with other two usb2 hard drive wd 320 and 250gb scorpio i don't have problem. It's an usb3 driver problem? or over capacity problem?  This problem occurred after a week of hard drive use.

I'm ****** off

Sorry for my english

What the heck is going on?

Upgraded to OS10.10 and now my FW externals keep dropping off every few days. I've run these fine for years under 10.7.5... finally made the jump to 10.10 and have spent the past month rebuilding multiple RAIDs only to have them drop off again without any explanation.

This is UNACCEPTABLE Apple.

Spotlight has never been enabled for the RAID's. Hard drives have NEVER been set to go to sleep. Just suddenly the drives are unreadable. I'm so sick of seeing Disk Utility report: Error: Disk Utility can’t repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.

WHY???????????????? What's the issue here????????

I've done a clean install. An SMC reset. A PRAM reset. Replaced ALL firewire cables. Replaced older HDDs in the RAIDs. Even sprung for the $130 for DiskWarrior (which saved me an entire rebuild ONCE but that RAID dropped off again a day later.) Added a NEW UPS for ONLY the external RAIDs and yet FW external RAIDs STILL keep dropping off.

The actual HDDs are a mix of Hatachi, Seagate, and Toshiba drives (no Western Digital anywhere). 5 RAID enclosures - 2 Oyen Digital Mobius and 3 Oyen Digital Datatale enclosures. 2013 MacPro 5,1.

Today I had an INTERNAL HDD get ejected while I was USING THE MACHINE. I have an internal drive set as a scratch drive for Adobe software. There's nothing on the drive. The drive is not used other than the background app usage Adobe assigns. I never even access the drive. I was surfing the 'net and out of nowhere that INTERNAL drive got ejected. How the heck does that happen???? An INTERNAL drive no less!!!!!!!!

Please correct this Apple. Please.

Yeah, I'm running into the same problem. I have a 1 TB external HD that was formatted as NTFS and had a bunch of movies on it. I know the drive still works because when I plugged it into a Windows machine, it was just fine.  No weird ejects.  When I plugged the same drive into my Mac running Yosemite, it would go into a mount/eject loop for a couple minutes until it just quit and gave up.  I thought it had something to do with the NTFS formatting, so I moved all the movies onto my NAS, plugged the drive back into my Mac and before it could unmount again, I quickly formatted it to HFS within Disk Utility. It did successfully format, but then went into the mount/eject loop again.  This is a powered external drive that I had connected to a powered USB hub that was attached to my iMac.  I removed the USB cable from the back port on the USB hub and put it on a front facing port and the mount/eject loop stopped.  Now, it seems stable until the computer goes to sleep.  Once it comes out of sleep, the drive is gone and I have to flip the power switch off and back on to get it to mount again.  My Time Machine external USB drive does not do this, but the only difference I can surmise is that my Time Machine is connected directly to my iMac, not through a powered USB hub.  Unfortunately, all the USB plugs in the back of my iMac are already in use, which is why I have the powered USB hub.  This is really strange.  On a side note, before I reformatted that drive, I had a Windows 7 virtual machine running under VirtualBox on my iMac and it didn't have any problem mounting the USB drive while it was plugged into the same port on the USB hub.  I firmly believe this is a problem with the software (OSX Yosemite). especially both Windows and my NAS were able to mount it without an issue.  Please fix it, Apple.

All my drives are formatted HFS+ with journalling and GUI boot partitions, always have been.

Having the same issue of disk getting ejected. I have a 2TB partitioned drive for TimeMachine and PS Scratch disks connected via a Ultra USB3.0 Dock. The disks drop off in the middle of a PS session or a copy operation or TM backup.

Have lost a lot of PS work so far

after trying everything, i believe it's a Yosemite problem too. no problems with externals prior to install, and error messages after install. two things that puzzle me post-upgrade : ironically, it's just my 3 lace externals and not my seagate. and, although unrelated, my iCloud photos are not syncing form phone/computer/ipad, but that's another topic.

I Solved my problem with a LaCie ext thunderbolt2 HD by switching to a LaCie thunderbolt 1 ext HD. The thunderbolt 2 ext drives with multiple drives have a hardware RAID. By switching to a thunderbolt 1 drive it does NOT have hardware RAID. My current drive is a Lacie 25TB thunderbolt configured with Softraid software to a RAID 5 volume. Currently working for 3 weeks now. Drive not backed up with time machine.