External Drive keeps disconnecting

I'm having this problem with a WD Ultra 1 TB USB 3.0. Never had a single issue running different USB 2.0 drives.

Steps so far:

1) Updated drive firmware

2) Deleted Time Machine plist file

3) Tried a different cable (from another USB drive that never disconnected on me)

4) Different USB ports, directly connected to the macbook and also in a powered USB hub.

And the drive is still disconnecting.

Interestingly, my problems with the drive seemed to start when I used the GUID option, but I switched it back to MBR (on another computer) and that didn't help. I've currently got it connected to another Mac and it's not disconnecting (usually was happening within 1 minute) so now I'm stuck with the thought that's it's a problem with this 2009 Macbook (the other box is a 2010 Macbook Air).

Additionally, I turned off the "put hard disks to sleep whenever possible" setting And, did a SMC and PRAM reset.

One thing I noted was that the drive never suts down *until* I get logged in to the OS. All during the startup, reboots, resets, etc., the power light stays lit. More evidence that this is a system problem and not a drive issue.

Hope my stream of consciousness troubleshooting isn't bothering anyone :-)

My disconnection *appears* to be somehow related to my user profile. Logged in as guest and then as an admin user I keep on the system and the drive stayed connected. Logged back in as my typical user and the drive stays connected for about 30 seconds tops. What could be in a user profile that would make a drive disconnect (while two other USB drives stay happily connected)? Ugh.

I Had similar problems to this on my mini 2012 model.

1 problem was the caddy the drive was in. The other was the available power.

I Now have two drives plugged directly into two of the USB ports on the mini.

Oddly enough the lights on the drive caddys now stay on and flicker during backups. Previous to the last OS upgrade they stayed off, but flickering during use as usual.

but whatever I'm sure its the same issue you have. Have you tried using a powered usb hub? And it has to be a good one. I tried a cheap one and it made matters worse, actually causing the system to shut down.

I'm having a "eureka" moment. It's the wddriveutilityhelper (or maybe wdhelper) application which I installed at some point when I was trying to get the drive to work as a readyshare/Time Machine and couldn't get Time Machine to see the drive. If the WD application is running, the drive will shut itself down even if the "sleep" item is turned off. If you install/run the application, it will insert itself in to your startup items.

I've given up on using the drive as a ReadyShare/Time machine though too. Seems that ability has left the buiding when Yosemite was released. Still, it will work as a Media file share drive connected to my Wifi Extender, which isn't a terrible thing considering it wasn't why I bought the extender in the first place.

Case closed (for me, at least).

Same here. Then I removed the (I'm sorry, this name is not going to be exactly accurate) wdddrivehelper from my admin user startup items. BOOM. Works fine now. Try it out!

External Hard Drive kept knocking off every time my Macbook Pro went to sleep.
Followed this handy video*, basically adjusting Energy Saver settings and we're all good:

https://www.youtube.com/watch?v=oDTmoVgkeGM

*Kayaking intro is an added bonus!