Q: External USB Hard Drive not showing up, after Yosemite update

I agree that my issue was different, but possibly related.  Perhaps over simplified, but there is a relation between functionality of external storage connected via USB.  To your point, it could just be a similar symptom with a different disease.  When searching for a solution to my problem, I found this thread.  Seeing that there are almost 15,000 views of this thread, I assume that there are many others with a problem like or near this.  I didn't intent to hijack the thread with a similar but different problem  -- this fixed mine, I offered in hopes it related enough to help some others. 

For clarification, my external drives did not show up in Disk Utility run from Recovery Mode until I went thru the cycle of the fix I highlighted above.  Once I went thru the steps of my fix, I could see the drives in Disk Utility, Finder, etc. 

An update - I was also able to see my thumb drives on my Air (13", mid 2013) after doing the fix.  The same fix worked with my Pro (13", late 2011).  I am helping someone out with their Macbook Pro (13", mid 2009), which also has a 3rd party hybrid drive.  All are running 10.10.1.  The 2009 MBP was able to read the thumb drives without issue and without doing the fix, so perhaps my SSD hypothesis was invalid. 

I'm curious is the path of Verify/Repair the disk & permissions followed by zapping the PRAM & resetting the SMC helped worked for anyone with the similar yet different issue?

I have two hubs - one trust and one unbranded.

Some drives work ok (more modern ones) on trust hub and others don't.

When I use both hubs I can get all my drives to be seen.

I have Paragon 12 NTFS manager

Not ideal - but works !!!

Hey Everyone,

This is not an encouraging read at all and the chances of your external hard drive working with Yosemite in the future seem very slim...

http://www.cindori.org/Trim-enabler-and-yosemite/

Seems Apple is not allowing third party drives to mount due to new security.  Not sure how I'm going to get the data off of my "third party" unauthorized drive and over to one that Apple deems acceptable...  Huge bummer.

Darn. So it is an anti-trust law issue after all.

My 2GB iPod Shuffle suffers from this now too, so I think that's pretty convincing evidence that it's not a third-party drive or anti-trust law issue.

My Garmin GPS, which previously mounted the internal "drive" as a device named "Garmin", now won't mount either --- but the "external" SDHC card in the GPS does mount.  Nothing changed on my iMac, except that I installed Yosemite 10.10.0, and then 10.10.1.  And both of them mounted just fine with 10.10.0.

Since both of those devices presumably have to work with both Macs and PCs, I assume they're all formatted as FAT32.

BTW, all of the above applies to my mid-2012 27" iMac.  In the case of the Garmin "internal" drive not mounting when I plugged the GPS into the USB on the iMac (via a Monster 24-port USB hub), it mounted just fine when I tried it on my early-2009 Macbook Pro, which is also running 10.10.1.

Methinks Apple has some code to tweak.

I found using bare drives in a dock that they work fine.  It may be an issue with complete enclosed drives having some software that is keeping Apple from letting them work properly.

Hello All,

I also was struggling endlessly attempting to get 4 external usb 3.0 drives contained in a drive dock to all be recognized plugged into a HighPoint Quad USB 3.0 Superspeed Raid HBA pcie card.

Very erratic behavior, sometimes two were recognized, sometimes not. When powered up in the dock one at a time, each time an additional unit was powered up, would receive system message that drive was not ejected properly, ugh!

So, attached drive dock to usb 2.0 port and all drives recognized! (great, except drives are 6gbs SATA III and now running at SATA II 3gbs).

Is Yosemite not able to deal with USB 3.0?

My drive dock (StarTech SATDOCK4U3E) has USB3.0 and ESata connectors. Hooked my dock up via ESata and all drives recognized and functioning at 6gbs!

Is ESata the answer until this issue is resolved? (Appears that way)

Hope this helps any others having this annoying and bothersome issue to deal with.

ooops!

Under ESata and Startech Drive dock drives are Sata II (3gbs), so back to base one.....

May have something to do with the current draw of all the drives at once

READY FOR THIS!?  A really stupid easy solution I found!  It worked for me at least.

I have a Early 2009 iMac 24inch upgraded to Yosemite.  Before I did I formatted a 1TB disk with the Mac file system and copied a few files - iPhoto library, music, some basic stuff.  So it wasn't an NTFS issue or anything.

Plugged the drive into the back of the Mac - NOTHING.  Considered third party software, etc but on a whim I plugged it into the side of the keyboard (essentially a USB hub) and voila!  It worked!  Crazy.  Annoying.  Got lucky.

Really hope this saves someone hours of time and frustration!

I have 2 internal Seagate drives. 1 750 GB and the other 1 TB. I house them in a Icy Dock enclosure and connect them with a USB 3.0 cable directly to my iMac. Neither have worked properly since the Yosemite update.

MY FRIEND FOUND A SOLUTION!

Sorry for the caps, but I'm really excited, because I need to have access to my external drive in Lightroom. I have no idea if this solution will work for you too, but it's worth a try. Like many of you, I had the option to view disks selected in the Sidebar, but it wasn't showing.

In the process of taking a look, a friend happened to run the cursor over the right side of the sidebar, like a vine wood wand with a dragon heartstring core. Straight across from where it says "Devices" on the left sidebar pane, the word "Show" magically appeared, like footsteps on an enchanted map. We clicked "Show," and lo and behold, the hard disk and external hard drive showed up in the Sidebar. I can now access the humming external hard drive through my Lightroom export drop-down.

I hope this helps!

Accidentally replied twice.

BINGO! This worked for me:

I took the black 3.0 USB cable from one of my 2014 external drives and plugged it into my old NTSF formatted external G-Drive.... and it then began showing up on the new Yosemite OSX Finder window.

Guessing the 2.0 USB cables dont work on the new Macbook Pros with Yosemite installed.

I had difficulty with my Mac mounting a 2GB external Seagate USB drive. After much trouble I found the solution was to enable NTFS write support for MAC OSX Yosemite. There is a video on youtube that walks you through the steps: https://www.youtube.com/watch?v=R-2NCRcylK0