Here is my process:

1. Go to Disk Utility and go Create Disk from Folder "File>New>Disk Image from Folder".  Choose your hd as the "folder" and save it to your desktop as something like "backup.dmg."  The dmg format should be "compressed." Hopefully you have enough space on your internal HD to do this. 
2. Once the image has been made go to Image>Scan Image for Restore and select the new DMG on your desktop and  hit return key.
3. Once this is done go into terminal and type the following: sudo asr -noverify -erase -source ~/backup.dmg -target /Volumes/MYEXTERNALHDNAME

This method erases your external HD but will create a bootable backup that migration assistant can read as well. If you are not wanting a bootable backup skip step three and just drag the newly created dmg to your external HD. It will be ready to clone back to your computer at some time in the future if need be.


ps: If you do not have enough space on your internal drive I would recommend use Carbon Copy Cloner to make a bootable image of your OS on your external. It can be set to no erase your external as well . . .

On Sep 22, 2011, at 11:42 AM, Larry Kost wrote:

I have a Macbook and have been trying to use the disk utility to make an image on an external drive (Segate Freeagent GoFlex drive).  I have upgraded to Lion.  When I try to create the image it seems to get through most of the process until it gets to the step where it says "Adding Resources".  It sits there for a long time (maybe 20 or 30 minutes) then says "Unable to create LarryMac.dmg error  -192".

Any ideas?  I looked on the web, but didn't find anything useful.