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I've got an external hard-drive caddy and a standard SATA IDE drive running my backups, archive and Time Machine.

It's started disconnecting seemingly randomly, always unexpectedly.

I get the standard 'Device Removal' warning, 'not properly put away'.

Recycling power makes it come back again.
I've taken it off a shared USB connection and plugged directly to MacBookPro USB port.
I'm going to test the drive on another box, but if it's a hardware problem on the Mac I'm wondering where to start.

The random timing feels like it might be heat causing this. Any tools to test HDDs and/or USB connection dropouts on a Mac?

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I've had exactly these problems with a WD mybook USB external, with no problems on any of my other external drives. So I long suspected the WD, but was unable to decisively track down where the problem occured; I'd be curious on the answer... – The Tentacle Aug 27 '09 at 14:49
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Does the external drive have its own source of power or does it use power from the USB port? – hanleyp Aug 27 '09 at 15:28
Yeah. It's a mains-powered caddy. Will take home at weekend and give it a thorough workout on Linux and PC and see if anything arises. I'm worried it's my MacBookPro so want to eliminate that possibility. – Michael Rose Aug 28 '09 at 8:27
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4 Answers

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Ok. This was a hardware fault. The caddy was designed in such a way that it became very easy to disconnect the cables inside with a small knock or nudge.

Boring, but solved.

Thanks all.

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I had the same problem with the USB plug on the hard drive enclosure. – mouviciel Dec 5 '11 at 14:50
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I have the same issues but with Lacie drives. The work fine connected to my iMac, it's just my MacBookPro.

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Does anything appear in the Console Messages section of Console.app?

Disconnections like this are most often power related (not enough power getting to drive) in my experience, although a bad cable or a failing hard drive aren't unheard of.

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Go to System Preferences → Energy Saver and untick "put the hard disk to sleep when possible".

That fixed the problem for me.

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