Anyone else having problems with external disks unmounting randomly/suddenly on Mavericks?

I am having the same problem its a 4TB Fantom drive and it keeps randomly ejecting

I'm having the same same issue.

3 volumes (in 2 usb HDs) disappear from the desktop,

but they remailn in the Finder sidebar.

However, after sleep, the USB2 Time Machine drive does not

return to the desktop or the sidebar.

Anyway to report this to Apple?

OS X 10.9

27" iMac, late 2012

nope, random HD ejects have been common for years on faulty drives but usually SATA bridge cards in HD enclosures.

common occurrence of a failing SATA bridge card

see here:

Your dead external hard drive is likely fine! Great hope for your 'faulty' external HD

I'm still running Mountain Lion, which has had the same problem with ejecting external drives with a message saying it had not been disconnected first. Turned out it was a faulty upgrade in early September. They finally released a patch which settled things down for a couple of weeks, but now it's happening again.

I have all new equipment - new Mac Mini, new external drives (Seagate, one powered, one unpowered).

So I also cannot see that this is because of faulty cards. I have been holding off upgrading to Mavericks on the grounds of "better the devil you know".

Not happy. all very well saying that random problems have been common for years, but this isn't random - it's frequent, on new equipment.

kharisma but now it's happening again..........So I also cannot see that this is because of faulty cards.

Seen it countless times, .....9 times out of 10 this occurrence is a faulty SATA card. Owned many 100s of HD and still own just under 100 of them.

You also just answered you own question with "now its happening again"

But if you dont believe me, thats ok 😉

Brand new equipment less than two months old.

Mac mini replaced after three weeks, so this one is only one month old.

Powered drive only two months old (Seagate).

Problem started with upgrade of ML released early September.

Stopped for a couple of weeks after recent patch.

Now it's happening again.

So the SATA cards on both the Mac minis are bad ... is that what you're saying?

I may have the solution to my own problem - about a week ago I bought a powered hub (USB3).

The powered external drive (USB3) is plugged directly into the computer (also USB3), but the unpowered drive (USB2) has been plugged into the hub.

I know from experience that some devices don't perform well through a hub. I'm going to leave the small drive unplugged unless I need it, and see if that helps.

Same problem here..Drobo Thunderbolt on Mac Mini worked perfectly until 10.9 upgrade. Now I am getting the same "the disk was ejected improperly" when waking from sleep.

I have the same problem (after upgrading) on Mac OS X 10.9 (iMac 27' late 2013, Fusion Drive 1TB).

The hard disk is 2TB / USB 3.0. (directly connected)

Here you can see the problem in action http://youtu.be/Zzss358cfKk

Yes, it is directly connected on the back of the (iMac) screen.

On OSX 10.8 everthing was just working fine. I also tested it, without any problems, on my old macbook pro (OS X 10.7).

I'm not sure what to do next.

Mybe another random event but

I read through this

C10. "Error: (-50) Creating directory"

or "error ... while creating the backup folder."

trying to fix this and my timemachine problem. By chance I changed my partitioning from the GUID to the apple partition table and my problems stopped. The drive that randomly disconnected over and over stayed connected and completed a full time machine backup. So far this has fixed the problem and the computers seems to no longer be locking when the drive is connected and disk util is functioning normally.

fingers are crossed.......