Tackle external hard drives randomly ejecting in OS X

HardDriveIconXA fault in OS X may exist for some users, where external drives unexpectedly eject and cause the system to display a “Disk ejected improperly” warning message. This usually occurs when the system is idling, such as when it is asleep, but at times may happen in the middle of file transfers or when browsing the drive for various files. When this happens, the drive’s view will disappear and all activity from it will halt, interrupting the transfer process.

Generally hard drives randomly ejecting suggests a hardware-based problem such as loss of power to the device or faulty cabling. As a result, the first step in tackling this problem is to try various combinations for managing power and connections:

  1. Plug devices directly into your Mac
  2. Avoid daisy-chaining
  3. Use a dedicated power supply for the device
  4. Use a powered hub for devices that do not have dedicated power
  5. Replace cables

Despite these approaches, you may find a drive will continue to eject, but when the same drive is attached to another Mac or to a PC, then it will be stable and not show the same random behavior.

If this is the case with your Mac, then unfortunately the problem may be in a nuance bug with OS X that has yet to be extinguished. In an ongoing Apple Discussion thread about this problem, numerous drives of different types, different makes, and different connections all show the same behavior. With no common hardware configuration to suggest a compatibility error, this suggests the problem is occurring from the way OS X is handling the drives.

As a result, while no universal solution has been found, there are several potential workarounds for this issue that may help stabilize your situation, before ultimately having to purchase a new drive to maintain stability:

Turn off background services that may regularly use the drive

Unless its power related, a drive randomly ejecting will come primarily from some program or service that is interacting with it. Unfortunately simply reading and writing to the drive is not the root cause of the problem, but doing what you can to reduce access to the drive will help prevent spurring of the underlying problem. Therefore, try adding the drive to Spotlight’s Privacy list and ensuring it is listed in Time Machine’s exclusion list (available by clicking the Options button in the Time Machine system preferences).

Turn off drive sleep and system sleep

Go to the Energy Saver system preferences and uncheck the option to put hard disks to sleep when possible. Be sure to do this for all power profiles (Battery, Power Adapter, etc.). In addition, drag the slider settings for system sleep to the far right so they are in the “Never” position, which will prevent the system from going to sleep. Note that for laptop systems, the Battery power profile will not have an option to prevent sleep; however, for Power Adapter you should have a slider or checkbox to prevent sleep mode.

Verify and repair your drive

An often overlooked issue with drives is the health of the partition scheme and filesystem. To check these, open the Disk Utility program and then hold the Command key and click the device name as well as any indented volume names listed under it to select them all at once. Then use the Verify Disk option in the First Aid tab to check the drive for errors. If any errors are found, attempt to repair them.

Turn off Encryption

If you have encrypted your external drive, then try decrypting it to see if the problem will go away. To do this, right-click the drive and choose the option to decrypt from the contextual menu. Once your password is supplied, the drive will begin the decryption process, which may take a few hours to complete, but when done, should reduce the layers of complexity through which OS X will access your data.

Uninstall drive management tools and drivers

OS X contains all of the drivers and services needed for accessing and mounting a locally-attached hard drive, so for the most part, hard drives you use with your Mac should not require any third-party drivers. Despite this, they sometimes ship with drivers that manufacturers recommend you install. If these are a requirement, then consider switching to a different device, but if not then consider uninstalling any drive management tools you are using. These are developed separately from OS X, and it is possible any small update to OS X could cause compatibility issues with these tools and drivers. If your drive is a special RAID array or other setup that requires custom driver software, then be sure you have both it and your drive’s firmware updated to the latest versions.

Format your drive

Granted this last approach is the last resort option, but is an often-overlooked detail. When you purchase a drive for your system, it will likely be formatted to FAT32 and perhaps have a custom partitioning scheme to work with different operating systems and provide you with backup software, drivers, and other offerings. While you should be able to use the drive as-is, the best approach is to fully partition the drive and format it freshly for use with your Mac, the instructions for formatting your Mac’s drive can be found here.

Even if you have already formatted your drive, problems may have cropped up that are not being detected by Disk Utility’s drive verification routines. These can be with the formatting, but also with some nuance configuration file or two that OS X stores on the drive, which may be the root of the error. Therefore, do what you can to back up all contents of the drive, and then use Disk Utility to fully partition and format the drive. When done, copy your data back to the drive and see if regular use of it is more stable.

32 thoughts on “Tackle external hard drives randomly ejecting in OS X

  1. HaX

    In my experience the Mac Finder warning “Disk Not Ejected Properly” arises due to lack of full compatibility of the external device. I mean, some devices generate such issue but others do not on the very same Mac. So, that is a hardware problem of the external device.

    1. HaX

      I meant that the failure may be on the Mac side sometimes, but other times it is in the external device, or on both. How to determine it:

      – Check the same external device with different Macs.
      – Check different external devices with the same Mac.

      For instance, LaCie external devices usually work with Mac without problems, but the ones from other manufacturers generate issues on all Macs on on some Mac models with the same operating system.

      1. Jeremycays

        I had numerous instances of this issue on a Lacie Thunderbolt drive. I replaced it with a WD drive and still had the same problem (though less frequently).

    2. M.Cox

      I had a perfectly functioning external hard drive under Yosemite that ejects about every 5 minutes under El Capitan, so not a hardware problem.

  2. Rick Auricchio

    I’ve found that various Seagate external models will misbehave, randomly disconnecting. This sometimes happens when the motor is commanded to spin down; the unit shuts down the electronics, causing a USB disconnect.

    Since the problem occurs with several Seagate models, I no longer recommend the brand to my clients.

    1. B. Jefferson Le Blanc

      Does the problem happen with “several” Seagate models on your Mac, and other Macs you’ve tried them on? Have you read reports of the problem with these particular drives from other users? If not, then the trouble may be with your Mac, not with the drives. I’ve read complaints about nearly every drive manufacturer. Every one has its partisans and its detractors. Which suggests to me that there is, in fact, little difference between them. As well, most manufacturers offer a range of quality in their drives, which may be a factor in failure rates.

      All that being said, I’ve had more problems with bridge failure in external drives than with the drives themselves. The drive case, which includes the bridge, is often made by someone other than the drive manufacturer. In some instances, as with drives from Otherworld Computing, you can get a replacement case when the bridge fails. Generic cases are also available and are usually less expensive than brand-name enclosures, though they provide fewer connectivity options. Even when the case is made by, or provided by, a particular drive maker, if the drive can be removed it can be installed in another enclosure. This happened to me recently when a Western Digital My Passport Studio drive failed. Western Digital does not offer replacement cases so I got one from OtherWorld – and the drive lives on.

      When an external drive fails I remove it from the case and test it with a NewerTech Voyager Q for 2.5″ and 3.5″ SATA drives. I also have a NewerTech USB 3 Universal Drive Adaptor that can handle ATA/IDE/ATAPI drives in addition to SATA drives. If the drive works with one of these devices, then I know it’s the connection bridge in the drive enclosure that died. Most people do not check a drive in this way, which means they could be blaming the wrong party when the drive appears to fail. I avoid, when I can, buying a drive that is completely integrated and cannot be functionally separated from the case. Usually, but not always, these are the cheap ones, where there is no way to open the case without breaking it.

      Undoubtedly people find it easier to just replace the entire external drive unit rather than going to the trouble of removing the drive from its case to test it. However, if you have important data on a drive that will no longer mount reliably on the Desktop, using a device like the Voyager Q or a drive adaptor is easily the least expensive and most effective way to recover your data.

      All this may seem to be only tangentially related to the issue Topher covers in his article, but since the real cause of the problem is so difficult to track down and may end up being impossible to solve with the procedures he recommends, ignoring the electronics in the drive bridge seems to me to be going only half-way to a solution.

  3. Kat Jenkins

    I feel fairly confident that this is an OS problem. On my Mac Pro, the problem never occurs if I am booted from a Snow Leopard drive. It always occurs when waking the system from sleep in Mountain Lion, Mavericks, and Yosemite. Same hardware, different result depending on the OS. I have been using a utility called Mountain from appgineers.de on the drives with later OSes and that has stopped the improper ejections.

  4. JiimC

    Wow — I had the “spontaneous disk ejection” problem several times yesterday, after never having had it before. So, I thought, what might be different today, causing this problem to come to the surface?

    For context, I’m running a late 2013 Mac Pro (the cylindrical one) under OS X Yosemite 10.10.5. My external disk (the only disk I have other than the 256 GB SSD that comes integrated into the Mac Pro) is a Thunderbolt-connected DataTale RS-M4T 4-drive enclosure populated with 4 WD server-class drives. Actually, when I encountered the spontaneous ejection problem, I had TWO RS-M4T enclosures connected (via two separate Thunderbolt ports on the Mac Pro) — i.e., not daisy-chained. I was in the process of copying very large chunks of data (200-700 GB) from a 2-drive RAID-0 array in one RS-M4T to a similar 2-drive RAID-0 array in the other RS-M4T. These copy operations are relatively speedy — somewhere around 300 Mbytes/sec. That translates to about 35 to 40 minutes to transfer one huge 700-GB chunk of data.

    So, back to what was different when I experienced the spontaneous ejections, compared to my more routine usage:

    (1) It was quite hot that day, and the room where my Mac Pro and drive enclosures live doesn’t have any air conditioning. It was also the hottest part of the day, around 3 to 4 pm.

    (2) I don’t often do near-terabyte copies such as those I’ve described above.

    (3) My Mac Pro is about 19 months old now. I use it every day and it’s probably had time to accumulate a significant amount of dust inside. As dust accumulates inside a machine, its cooling performance will likely deteriorate (impeded air flow).

    (4) I was using 3 Thunderbolt ports simultaneously (2 for the two RS-M4T’s and 1 for my Thunderbolt video display).

    (5) The speed of the transfers was boosted by the fact that I was reading from one RAID arrray and writing to a different RAID array in a different RS-M4T enclosure.

    I don’t think I saw any instance in which a spontaneous ejection occurred before reaching about the 200 Gbyte mark during a single copy.

    So, my current #1 hypothesis as to why my drives were spontaneously ejecting relates to HEAT. I.e., perhaps after running a continuous copy operation at extreme speed for a long enough time, something gets hot enough to cause an error. It could be in the drive enclosure electronics, or in one of the drives, or in the Thunderbolt port hardware of the Mac, or … etc.

    This is, of course, only a hypothesis. And it probably wouldn’t explain spontaneous ejections that have occurred in other scenarios, as reported by other commenters.

    1. Len B

      I think you are on to something with your heat hypothesis. I reached the same conclusion and address the problem with a cheap fan and the problem disappeared immediately.

      My problem involving disappearing external drive magic act began a few weeks ago after two mirrors got corrupted during a brown-out. Every rebuild attempt failed anywhere from minutes to hours in. My RAID volume would suddenly eject for no apparent reason. I spent hours researching the issue and tried every solution here and a few more. Then I read your post concerning heat. Sure enough, my drives were getting really hot in their enclosures during the rebuild process – I mean really hot, hot enough to leave marks when my arm brushed against them.

      I guess it took having two mirrors go bad (so four of my six 2TB G-Drives disks screaming away – in the summer no less) to finally generate enough heat to cause a problem. A cheap fan in front of the enclosures to provide an extra ventilation boost during the rebuilds did the trick. Enclosure temps easily dropped 40 degrees within a few minutes. They are now cool to the touch even during the most strenuous activity. Problem solved – no more random improper disk ejects.

  5. MikeWL

    This started happening immediately upon my upgrade to El Capitan… This is an OS issue. I have 2 drives that are different brands and BOTH started doing this right when El Capitan was installed… it is an OS problem… definitely.

  6. Jay

    My problem started with El Capitan. Previous OS had no problems. I am using a USB 3 hub. However, I am able to remedy the situation by plugging my USB drives directly into my Mac Mini.

  7. Donna

    This may be a silly question, but… I know if a disk is improperly disconnected (including by randomly ejecting), that can cause corruption on that disk. But can it cause problems with the computer as well, such as with the file directory? And if it did cause problems with the computer, would those be limited to how it relates to the disk in question?

  8. Jim Gleeson

    Been having the spontaneous ejection issue on an external WD 4 tb hard drive as well on my cylindrical Mac running El Capitan and it seems to be having trouble from time to time with other thunderbolt related peripherals as well as the usb. Examples of this over time are I have dual monitors and occasionally one will not “activate” Usuallly the unplug/replug thing works but other times it has been more stubborn and required a restart.

    I have a drobo that has dealt with Ejection issues on and off since I don’t know when (I think it was sleep related), but this WD drive just started doing it recently while bouncing a podcast . My solution in the past has been to unplug and replug cords into other ports and the problem seems to resolve itself, for awhile. But tonight I watched the Hard Drive constantly mount and eject and it moved from mere annoyance to nearly unusable. I have run some diagnostics on it and it checks clear…right before it disconnects again. Right now it appears to be running okay, but I just wanted to verify this issue right now on my computer.

  9. JD Stillwater

    Same problem; external WD “My Book” 4TB disk drive. Ejects itself when computer is idle or asleep. Unplugging and re-plugging USB doesn’t do it; have to unplug the drive’s power AND USB to remount.

    I am running Yosemite (10.10.5) on a mid-2012 MBP. I had hoped upgrading to El Cap would fix this. Sounds like maybe not…

  10. Blancho

    Lacie Thunderbolt Drive doing exactly the same. About 20 times today. Never had the problem when plugged into my new Mac Pro. Apple Support tried to convince me that it was a driver issue for a Wacom Tablet. Utter Rubbish. Sick and tired of this happening as it’s badly impacting on my workflow.

  11. Ken Collins

    This is definitely an OS X quality issue. I have an iMac that is always on and never sleeps. It has two external drives (Firewire through an Apple Thunderbolt adapter), a network share mounted over ethernet, and a device that is not a drive. I never had a problem until El Captain Crunch (I call it that because of the puerile UI and dumbed-down utilities). It happens with my MacBook Pro so often that I can’t use the Time Machine.

    Sometimes during the night, ALL external drives unmount, including the device that is not a drive and including the network share. There are two NASs and half a dozen computers, tablets, and phones on my network. If my 200GB internet connection or my router had gone down, I’d know. The network did not go down.

    This is not the solution: do the few disk utilities that remain on Captain Crunch, move the data off a 3TB disk, reformat the disk, put the data back, change all the cables, reconfigure the iMac so the data and power cables aren’t within six inches, and you’ll get the same problem because that makes a good column but is not the solution.

    This is the solution: gather the other peasants, storm the Apple castle with torches, convince them that we are grown-ups and use our Macs for grown-up purposes and demand that their products actually work. I keep wondering what brand of computer they use in their offices, because if they used Macs, these problems would have been fixed long ago.

  12. Steve

    I’m running 10.11.5 on a 15inch Mid 2015 MacBook Pro, and my USB 3 SSD drive disconnects after random idle time but there are no error messages. I can still see the mounted drive in Finder but when I click on it it appears empty. I can’t disconnect it at that point, and the finder basically freezes. The only way out at that point is to yank the USB 3 connection at which time the “improperly disconnected message” pops up and I can reconnect and go about my business. It’s pretty frustrating.

    The other craziness is EVERYtime I reboot my machine, my 2 externally connected monitors (27″ Dell monitor via HDMI and a 19″ samsung via a thunderbolt to DVI adapter) show black, while the laptop screen shows the desktop background with no login prompt. I have to disconnect both monitors which causes the log in prompt to appear on the laptop, then I log in, then I reconnect the external displays and the 27 becomes my master which is what I want. It’s very frustrating.

  13. Robert

    My experience has been the simultaneous random ejecting of the flash card message of improper ejection along with a message that the card has been mounted successfully! I suspected the reader which is a USB 2 plugged directly into the back of a late 2013 iMac. Changing readers to a Lexar USB 3 Reader solved the problem not only for the flash cards but also for thumb drives that happen to be running at the same time. Both card & flash drive have been opened for over 30 mins. Hopefully adding this to the list of solutions will help others and well done Lexar!

  14. David

    I started having this drive ejecting problem after installing a Caldigit USB 3 / eSata PCIe card in my 2011 MacPro. Tech support from Caldigit confirmed that this is an OSX issue:

    “Unfortunately the issue exists because of changes Apple made to OS X. Apple no longer manufactures computers with physical PCIe cards so the newer OS X versions are designed to cut power to the PCIe slots when put to sleep. This is what is causing your drives to get ejected. Unfortunately the Pro card is reliant on Apple drivers so there isn’t anything we can do to change this behavior. The only thing that we can suggest is for you to dismount your drive before putting your computer to sleep.”

  15. Martin

    Six external drives running without problems under Mavericks. I just “upgraded” to El Capitan and get the first disk ejection while Migration Assistant was pulling in files from the backup drive. After several attempts, I got all the files transferred but I wish I hadn’t bothered. Each time Carbon Copy Cloner runs, the target drive dismounts after five minutes. I’ll have to go back to Mavericks. It was bad enough but this problem is worse!

  16. Ellis Vener

    Over the past few weeks I have had this problem as well and it has been increasing in frequency. By yesterday it was up to several times a day. My theory is that that there is some error in the USB driver code.

    After following the articles guideline’s about what to do and still having the problem, I tried something different: Instead of connecting the drive directly to my computer’s USB 3.0 ports I connected it to the computer through my OWC Thunderbolt 2 Dock. It has been nearly 24 hours and the random ejection problem has not re-occured.

    I am not flogging the OWC hardware. if my theory about the problem being a bug in the code is right, connecting through any other brand’s Thunderbolt hub/dock (CalDigit or Belkin, etc.) will solve the problem too.

  17. DK

    I’d like to add a posible solution to a similar issue. I had my mac keyboard plugged into Macbook Pro and from the keyboard I had a 64GB flash drive plugged in and then a 4tb external drive (WD My passport Ultra). It started ejecting my drives instantly and non stop. I tried verify disk utility on external and then repair drive and nothing. Finally some random message popped out luckily that the power from keyboard cannot handle both drives. Once I plugged in external directly to laptop and took out usb, all is perfect. I know this is a side issue, but maybe it’ll help.

    1. Ellis Vener

      That is interesting DK! So it might not be an OS X issue as a hardware power supply issue to the USB ports! That makes sense to me.

  18. Ashlea

    The HDD on my mid-2012 MBP recently died and I have had it replaced, in the meantime rescuing old data with Genius techs onto a brand new external LaCie as purchased in an Apple store. All of a sudden, not even two weeks old I am having similar issues as described above. The drive seems to mount, is visible on the desktop and in finder, but does not seem to load anything within it. When I go to “Get Info” it recognises that there is data on the disk, but again it is actually inaccessible. Although it will try to load data it eventually just gives up, finder freezes and I get the error message about disconnecting. I tried on my husband’s MBP and it loaded data once, but now it is doing the same thing. I’m at a loss because I hadn’t backed up when my last HDD went, saved it all with the new LaCie drive, now have been so busy in the last two weeks it is not backed up elsewhere, but cannot manage to access what is now on LaCie. Arhhhhh!

  19. Blake Henderson

    In case it’s useful to anyone….. I am having the same issue with my Macbook Pro and an external Lacie Thunderbolt drive. The problem has never occurred until today, which happens to be the hottest day I can recall. After reading one of your observations, I put a small fan against the back of my Macbook. Voila! the drive remains attached! So at least in my case, temperature seems to be related. Just to confirm my hypothesis, I have repeatedly removed the fan…. each time the drive ejects automatically after a couple minutes.

    Ive read numerous threads about this topic and I’m not seeing anyone mention temperature as the problem. Strange.


  20. Sue

    Just been reading through these posts because I’m trying to find out if other Mac users experience the spontaneous ejection of an external hard drive. I am fairly new to Mac and have been slowly re-learning my computer skills since April. I had a few teething problems at the outset but Apple support helps in each case, especially with the twice weekly frozen screens (not really expected on a brand new computer!!)
    I’ve just experienced my 3rd spontaneous ejection since April of the HD I use with the Time Machine.
    It has me totally confused and I couldn’t even ‘find’ the device even though I disconnected it from the Mac and mains then reconnected it. I would have expected it to show up in Finder but it didn’t.
    So I started a chat session with Apple support….. we painfully and slowly went through the usual Q&A’s (it was VERY busy and the help-desk supporter kept apologizing for time lapses!) I took it upon myself to remove the cable from the HUB of 4 I have been using for donkey’s years and reconnected to a cable extension I have running from the back of the screen. As I am limited to just 3 ports, these are obviously filled with printer/scanner, small USB 3 way splitter and card reader (saves me trying to find the slots in the back!) and my own invention of having an extension cable running from the back so I can plug in my devices without having to tear everything off of my desk to get to the back of the screen.
    The HD immediately connected and the Time Machine started running again and I’m thankfully all backup up once more.
    What I fail to understand is why the HUB connection suddenly failed. I have my Apple keyboard attached to the same HUB of 4 of which only two were in constant use. Apple support said this does happen from time to time on a random basis and they can’t do anything about it but suggest I purchase a new HUB.
    I might reconnect the backup HD again to the hub (a different port maybe) and see what happens.
    I was transferring data from my Mac to a different external HD when this happened. That HD was NOT connected to the HUB but to my makeshift extension running straight into the Mac.
    It’s very odd especially now I’ve been reading other Mac users experience similar occurrences.
    I run El Capitan 10.11.6 by the way.
    And I don’t believe my problem to be heat related especially since we are now nicely in the throws of Autumn temperatures. I had no problems earlier this year when the outside heat soared above 30C!

  21. Kenko

    I recently encountered this problem as wel. My external harddrive from Transcend worked flawless before, but suddenly gets ejected randomly. The issue was resolved by simply replacing the USB cable. While working with different drives I switched up the original cable with a cheap cable that came with a cheap case. The “bad” cable was the culprit. It didn’t even have the “SS” superspeed logo.

    Now everythings back to normal. So try switching to a higher quality USB cable.

    Hope this helps!

  22. Sharath Raju

    I faced the same issue on a Toshiba v63700 external hard disk drive. I did a “First Aid” using Disk Utility and this resolved the issue (so far).

  23. Sue

    I have 1 drive that is partitioned into 3. I can have so many disk eject errors I have had to start shutting down my machine daily, rather than putting it to sleep. It was taking me 20 minutes to close all the errors. It never did this until the new OS, and updating to 12.12 has not helped, if anything, it has made it worse as not the disk ejects when it is in use. Come on Apple, Fix this stuff!

  24. Robert C

    I agree that the problem lies in Mac OS and that turning off Spotlight and Time Machine for external drives is a good thing to do. Checking the drive with Disk Utility is always a good thing to do. Spending bucks on the OWC dock is ok if you have lots of bucks, but the BEST solution (IMHO) is the one given by Kat Jenkins, to buy Mountain from appgineers.de for $6 (a whole lot cheaper than the OWC dock, unless you need the dock anyway) and VERY flexible and does stuff that for some reason Apple did not put in their OS. FWIW, I think Apple is gradually deteriorating due to lack of OS quality control compounded by their increasing disregard for users hardware concerns, but that is another issue. In the meantime, till they wakeup to the fact that they need to facilitate the needs of power users, third party fixers have a great opportunity to assist us and THANKS to those who share these useful apps in public forums such as this one so we can find solutions to problems with OS X that waste our time and discourage us.

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