External USB Hard Drive not showing up, after Yosemite update

From the sound of this entire discussion, it appears that Yosemite has problems recognising external Windows-based filesystems connected through USB.

I tried connecting a 320GB Western Digital "Passport" drive, formatted as FAT32. The Finder reported the drive as unreadable, and offered to format it, eject it, or ignore the message. I ignored, and Disk Utility saw the drive, but the volume was greyed out. It was reported as "exFAT" which is wrong: it's FAT32, and had just passed chkdsk on a Windows 7 box, which reported it as FAT32. It being completely mis-diagnosed in the first place, I was not surprised that verifying or repairing from Disk Utility failed. Reboot did to help.

Having googled around I found this http://www.reddit.com/r/osx/comments/2ehws5/os_x_1010_yosemite_beta_2_possible_b ug_fat32/ and did the following:

jjp@Torus:/Volumes $ sudo su

Password:

sh-3.2# mkdir /Volumes/test

sh-3.2# mount_msdos /dev/disk#s# /Volumes/test # replace "disk#s#" with the correct name as reported by Disk Utility

To my surprise, this worked: the drive showed up on the desktop and in the Finder sidebar and was usable in read-write mode. Disk Utility, however, still had it greyed out. There are other things wrong, too: "ejecting" did not work (it reported the drive as being used), and after either "force ejecting" or manually unmounting

with sh-3.2# umount /Volumes/test the icon remained on the desktop, though not in the Finder sidebar.

It seems that even though the basic functionality of mounting a FAT32 seems to be OK, all the bells and whistles are still broken.

This is not a trivial problem. There are a myriad of cheap devices out there which have FAT32-formatted storage on them, whether it's memory sticks, flash cards or our cats' GPS trackers. None of these can be naturally expected to work on this new £3400 computer without superuser hacking. Honestly, come on, Apple!

Yosemite 10.10.2 on Mac Pro (Late 2013).

Hey, msohni, thanks for adding that write-up of the problem. It seems like a good summary. I'll only add a couple comments.

1) The last sentence of your second paragraph says, "Reboot did to help." Did you mean to say, "Reboot did *not* help"?

2) For me, a reboot always (so far) clears up the problem, temporarily. By "temporarily" I mean, for about 2-4 unmount/disconnect/reconnect/remount cycles. For example, as I've stated (several times?) on this thread, I have a new iPod Shuffle that I use on my (mostly) daily 4.5-mile walks. On about the 3rd or 4th time I reconnect it on my iMac when I get home from my walk, Yosemite refuses to mount it. It shows up in Disk Utility, but the "Apple iPod Media" partition is greyed out. I also have a Garmin GPS with an external SDHC card that contains about 14 GB of music files on it (this particular model of GPS has a built-in MP3 player, so it is the source of the music I listen to while I'm driving). Every time I get home from going anywhere, I download the GPS track files from the built-in memory on the GPS onto my iMac. On about the 3rd or 4th reconnect the internal GPS built-in memory fails to mount. So far, the external SDHC card on the GPS *does* mount consistently. That doesn't help me, of course, because the GPS track files I want to download to my iMac are on the built-in GPS memory, which fails to mount. When this happens, I have found that rebooting the iMac *always* (knock on wood) restores proper connect/mount functionality of these two external USB memory devices, but only for about 2-4 reconnections. This also happens on my early-2009 Macbook Pro. Both machines running OS X 10.10.2.

When these two devices *do* mount, Disk Utility thinks the partitions are "MS-DOS (FAT32)". When they do *not* mount, Disk Utility thinks the partitions are "ZFS File System". Obviously that is not correct and may be a strong hint to Apple developers as to where they may find the bug that is causing this problem.

3) A bonus comment: Would you please post your comment to the Apple OS X feedback page? There have been comments elsewhere on this (and other) threads to the effect that Apple doesn't necessarily look at comments posted here. Rather, this is supposedly a "user-supported" forum so it may be a lot of "preaching to the choir", whereas the feedback page supposedly is guaranteed to be seen by Apple personnel. The Apple OS X Feedback page is at http://www.apple.com/feedback/macosx.html

I have posted comments about this issue to that feedback page a couple times, but the more people who bring it directly to Apple's attention, the more likely it is that they'll do something about it.

1) Yes, that sentence was meant to be either "Reboot did not help" or "Reboot did nothing to help" - the final post got stuck in the middle between the two!

2) Even after reboot, the WD volume was consistently seen by Disk Utility as "exFAT", and did not mount. As I wasn't about to play around with the drive itself (such as reformatting it to make sure that Western Digital got things right years ago), I had to leave it at that. Various memory sticks did get recognised properly.

I share your opinion that the underlying bug must be that the file system is not recognised correctly. In my case FAT32 -> exFAT, in yours FAT32 -> ZFS.

3) Done!

Another thing that was mentioned in this thread was that when waking up from sleep, the system sometimes complains that an external drive had not been ejected properly. That appears to be a separate problem, independent of USB, because it happens occasionally to me with an HFS+ formatted Firewire 800 drive, hanging off a Thunderbolt port via an Apple-original adapter cable. No USB in that mix. It has so far not happened with my genuine external Thunderbolt RAID drive.

For my hard drive that doesn't show up at all, the problem is not Yosemite per se. It's the USB3 driver incompatibility. Try using a USB2 cable (micro USB just like an android charger cable that plugs in half of the slot on your hard drive) and it will work. Or try connecting it to an older computer that has USB2 ports on it (with the original USB3 cable) and it will work BOTH on Yosemite and Mavericks. Of course it will transfer data at USB2 speeds. Apple screwed up the drivers again so we have to wait for them to 1. receive thousands of complaints 2. wait for eternity to acknowledge there's an issue. 3. take their sweet time fixing the USB3 drivers. Until then you can get by with USB2 cables. I hope this helps!

Just for grins, please try an experiment and let us know how it goes. The experiment is to unmount/disconnect, then reconnect the external hard drive using the USB2 cables. Do this without shutting down and restarting, or rebooting the computer. See how many times you can do that before the hard drive won't mount. For me, it is about 2-4 times with my external Garmin GPS and iPod Shuffle, both using USB2 (since that is what my mid-2011 iMac and early-2009 Macbook Pro support).

I have a suspicion that everyone who has reported "solutions" to the problem aren't routinely unmounting and disconnecting, then reconnecting their external USB hard drives.

In my case (3TB Seagate Backup+ on MacOS 10.10.2 2014 Macbook Pro15, all USB3 ports and cables) the hard disk doesn't show in Finder, Disk Utility or with "diskutil list" in the terminal or even in recovery mode. It doesn't show in start disk, with several restarts and resets and many other things I tried. Even the Console doesn't react to the drive being inserted (with a USB3 cable). The hard drive starts spinning but the OS doesn't even pretend to acknowledge it! I tried all the resets, updating firmware, formatting with different file systems and many 3rd party tests and diagnostics. I even installed non-generic usb controllers on Yosemite without any success.

At last, I took it to our IT department and tried it on many different combinations of OS, USB ports and cables and concluded that it's USB3 driver in Yosemite that's not reacting to the hard drive USB3 connection. It worked perfectly fine on an older macbook pro with USB2 ports and the latest clean install of Yosemite, also on a new macbook pro with the microUSB2 cable (final solution for my own new laptop), but it wouldn't work on anything with Yosemite and USB3. All the articles and fixes I read so far assume some sort of recognition at some level (from terminal or DiskUtility or Recovery mode) which was simply not the case with my hard drive. I'm confident at this point that the problem lies with Yosemite USB3 drivers not recognizing (or even reacting) to the USB3 connection on the hard disk. There might be a firmware update from Seagate/WD/etc. to address this problem but I'm not too optimistic. I think Apple should make its drivers compatible with these mainstream hard drives.

Hey Aboozar2010, you are describing the exact issues I am having. I just got a new 2014 MBA to replace my 2011 MBA. After saving my data on my 2011, I attempted to transfer the data to my 2014 with no luck. Both Macs have the latest 10.10.2 Yosemite. The 2011 MBA has USB 2.0 while the 2014 MBA has USB 3.0. Everything works perfectly fine while plugged into the 2011. When I plug in the drive to my 2014, the drive spins but never mounts to the desktop, finder, or disk utility. Applecare could not trouble shoot this issue over the phone today. I will post an update after my appointment at the Genius bar this week. I also believe that this is a USB 3.0 driver error on the newer Macs because my 2014 MBA mounts all USB 2.0 devices Hard Drives. I also tried to download the latest firmware from the WD support site with no luck.

If i can help anyone,I have had an Issue with my Seagaye 1TB drive for 2 weeks now, I repaired the disk in diskutility and with diskwarrior several times(took forever) before i solved it. It has the Mac OS extended filesysten. I simply put the USB3 cable into a USB2 hub and voila, the disk worked again. Than i ran Diskwarrior and rebuild the library and fixed damaged files, After a restart i plugged it in with the USB3 cable and everything works!

I can get external USB drives to mount too. Where the problem manifests itself is when you unmount/disconnect/reconnect several times (like with iPod shuffles and Garmin GPSes). On about the third or fourth reconnect, the devices will fail to mount. I suspect that many people who have added comments like yours think that they've found a solution, but I suspect that is mostly because most of them don't unmount/disconnect/reconnect their devices very much after they're up and running.

If you dare, please try that unmount/disconnect/reconnect operation on your Seagate USB3 drive a few times and let us all know how many times you can do it before it fails to mount. When it fails to mount, rebooting/restarting the computer seems to reliably restore the ability for it to mount. If you're like me, it's a PITA to reboot/restart the computer, but it would provide some good data on where the problem in Yosemite really lies.

Well, i did what you said, and my 1 TB Seagate Backup Plus drive works perfectly fine now with mounting and unmounting. I tried for about 6-7 times, all good. I guess there has been a lot of posts here, but i can just share what i did - and for me it rescued what i thought was a broken hard drive. Putting the external hard drive into the usb2 connection and rebuilding the directory worked here. I don't have any other usb3 devices to test with. Good luck!

Thanks for the response. Do you also get USB3 speeds? My problem occurs with a USB3 port AND a USB3 cable. If I plug mine with a USB3 cable to an older USB2 port, or use a USB2 cable with my new Macbook Pro UBB3 ports, both work fine (but of course w. slow USB2 speeds). I wonder if what you did made it possible to mount a USB3 HDD to a USB3 port and use USB3 transfer rates.

i am not familiar with Diskwarrior, but "rebuilding the directory" is something that diskutility (i.e. the UNIX fsck program) *should* be doing. Just out of interest, when you look at the lost+found directory at the root of the mounted drive from the command line, do you see any contents? Like thus:

machine user$ cd /Volumes/<disk-name>

machine:<disk-name> user$ ls lost+found

<lots of file names with funny numbers as names>

The presence of files in this directory indicates that there had been corruption that was fixed, by fsck, with some lasting damage (files lost).

This is my read and write speed, and i do get them with a USB3 cable and USB3 port. Have you tried a disk repair with the usb2 cable, and then try the USB3 cable?

Mshoni - i get in terminal that the folder cannot be found. This is my report from diskwarrior when fixing the External hard drive with the usb2 cable

I fixed mine by connecting my seagate external hd into a windows machine and deleted the partition. The moment I connected it back into my MacBook Pro 15" Yosemite it was recognised. I deleted, reformatted and it worked. Whew!