I had a 3 TB external hard drive with two existing partitions -- let's call them "foo" and "bar." I didn't need foo anymore, so I clicked on the "Partition" tab and the minus sign button. Disk Utility informed me that my foo partition would be erased and my bar partition would NOT be erased. After committing the change, it seemed to do what it promised; there was no longer a "foo" partition listed and the "bar" partition was sitting in the middle of the hard drive. Not able to resize the bar partition in Disk Utility to take up the entire 3 TBs, I decided to allocate a new partition to the new free space that had been created where "foo" used to be with the intention of copying data over to the new partition. I clicked once on the free space area, and clicked the plus sign button. Disk Utility informed me that a new partition, let's say I named it "newfoo" would be created and other partitions would not be affected. When I committed, what did I see? Two partitions, the top one called "newfoo" and the bottom one called "bar?" No. I ended up with a top partition called "disk6s2" and the BOTTOM one called "newfoo," the latter which had overwritten "bar" and the files that were in bar were not in "newfoo." At this point, you might be wondering what my question is. In fact, it isn't a question at all, but an admonishment. DON'T TRUST DISK UTILITY. I don't know why there's a partition called "disk6s2" and I don't care. The point is, if you're going to use Disk Utility, pretend you're pushing a button that instead of "Apply" is called "Do unexpected crap that might blow away existing data."