When iMac sleeps... it shuts down external hard drives

When I wake my iMac I get the error message that my hard drives were removed, could cause damage, etc. This just started today. It's almost like the iMac kind of goes into a deeeeeeeep sleep... but the computer doesnt shut down totally. I can still wake it, takes a little longer than usual though.
Anyone know what the issue can be?
Thanks

Do you have an external drive attached?
The reason for asking is I have seen similar errors when I fail
to properly unmount or removes an external drive.
There may be a better way but when I want to turn off my
external drive (used for TM and SD), I right click on he
external HD's icon and select the EJECT option. This unmount
the drive so the power can be turned OFF and removed
from the back of the iMac. You can also do with the Disk
Utility.
Try unmounting your external drives and restart to see
if this helps.

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Sorry for not responding sooner, I support your position completely - as for the external drive I assumed that the individual was a previous mac user and knew about that (my mistake) at home I have a couple of external drives
one drive is acknowledged regardless of format (mac/win) its a partitioned drive.... the other one - far as the mac is concerned does exist when i connect it. I believe its a win only drive (will have to check the specs on it) but it works on the win-notebooks.
so my point of reference was coming that perspective, with no additional posts I have to assume you had the correct answer. have a great day.

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This happens often because the processes that run over the MacOS, but the power was not enough to power your device. Actually this happens with external hard drives on any platform. Sometimes the USB port is not enough or even energizes permissions MacOS fumble.
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When I download videos (from an external hard drive), they appear to be downloaded (file sizes look correct) but they all stop playing a few minutes in!

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Upon rebooting, my iMac 3.06 GHz Intel Core 2 Duo with 4GB RAM, running OS X 10.5.4, locked up in a gray screen, the "gray screen of death."
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Raja,
Do a SMC reset perhaps even a couple of times and see if that helps. Also in System Preferences + Startup Disk make sure the internal HD is selected.
SMC RESET
Shut down the computer.
Unplug the computer's power cord and all peripherals.
Press and hold the power button for 5 seconds.
Release the power button.
Attach the computers power cable.
Press the power button to turn on the computer.
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Shut down the computer.
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Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
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i've been using a LaCie external hard drive as my timemachine back up for several years without incident. a few days ago i unplugged the lacie and when i plugged it back in, imac could no longer recognize it. when i go to time machine and try to"select disc" it tells me there is none to select. when i go to system prefs disc utility i can see the lacie icon in the left column, but when i click on it i just get the spinning beachball forever, and have to force quit. any thoughts?

Your HD might be corrupted, try going to spotlight, look up "Disk Utility" select your external and verify disk, there might be some errors on the disk, if so, then click repair disk, try that and get back to us.

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I've been using a Seagate external hard drive to back-up everything from my old laptop. I just got a new iMac and plugged it in (via USB) and it's not recognizing it. I can't find it in the Mac system. I'm not super computer savy but on other iMacs I've used when I've plugged in something external (iPhone, camera card, thumb drive) it pops up right away.
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So what is the APPLE HDD?
Here is a screenshot of my devices on my iMac:
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Can you post a screenshot of yours?

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The drive does not appear in Disk Utility.
And I don't think I'll be installing DiskWarrior until Leopards countless bugs are fixed, especially after reading THIS:
Alsoft: There are some DiskWarrior "compatibility issues" with Leopard
After previously stating "you can run the (current version of DiskWarrior under Leopard) knowing no harm will come to the hard drive or to your data," Alsoft has now posted a message to its Web site stating "there are some compatibility issues when running an installed copy of DiskWarrior 4.0 while started up from Mac OS X 10.5 Leopard. Alsoft currently recommends that you do not run DiskWarrior 4.0 while the computer is started from Mac OS X 10.5 Leopard."
http://www.macfixit.com/article.php?story=20071026153956503

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When trying to copy files (itunes music folder) to an external hard drive, I get the following message: Copying music failed. An unknown error occurred (-50).
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Gary,
A couple of posts referencing "error -50" seem to indicate that the error could result from a corrupted file.
One from Kappy follows:
Error -50 Post
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Bob

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I plug in a Toshiba 500 Gb External Hard drive and it doesn't show up on the desktop, in the finder window or in Disk Utility. It shows up in all those places on my work iMac and my son's laptop. Any ideas why my computer doesn't recognize it? Thanks for any help.

donna226 wrote:
It connects with a USB 3.0 cable but states that it is compatible with 2.0 as well.
USB3 is downward compatible with USB2.
Flash drives show up when plugged into the USB ports of which there are four. The power indicator light on the drive is on and I can feel the drive spinning.Tried doing a smc reset and it didn't help.
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The drive will spin down if Energy Saver tells it do so in Apple menu -> System Preferences -> Energy Saver. I have found though, spinning down an external hard drive sometimes is not desired because Energy Saver may not be able to give back all the power the drive desires when it wakes up. This can lead to an improperly dismounted volume causing occasional directory damage. My suggestion is to simply dismount it, and leave Disk Utility up so you can mount it again. Disk Utility is in Applications -> Utilities folder.

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managed to solve it myself after reading some other information on other forums.
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I have backed up my disk using Time Machine. I then deleted the back-up files from my MacBook hard drive.
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Hello,
Time Machine is not a good way to do that, when it eventually needs more room it deletes old Backups to make room.
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I have bought an USB external drive but my Imac does not recognize it,
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characteristics of the disk
toshiba, 1TB, USB 3.0
thanks

The problem is NOT the fact that it is a USB 3.0 drive, as USB 3.0 is backwards compatible with USB 2.0. The problem is specific to Toshiba Canvio portable drives. They only work if you use a micro-USB2 cable instead of the included USB 3.0 cable. This problem does NOT affect other USB 3.0 portable drives (Seagate, Western Digital, etc.), and they work fine with USB 3.0 cables.
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See Mac OS X: "Broken folder" icon, prohibitory sign, or kernel panic when computer starts
http://docs.info.apple.com/article.html?artnum=106805
 Cheers, Tom

When iMac sleeps... it shuts down external hard drives

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