Don't trust Disk Utility

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."

SandboxGeneral said:

Somewhere in your process you must have missed a step or clicked the wrong partition.

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Since I don't have video proof, I know it'll be impossible to prove that I didn't slip up somewhere. But I definitely remember left-clicking in the free space area and Disk Utility not mentioning at all that it would touch the "bar" partition. It's plausible that the exact combination of file system(s) and steps I took happened to expose a bug in the UI.

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simsaladimbamba said:

In all my uses of Disk Utility and formatting around 50 HDDs, even partitioning them and only erasing one of ten partitions on one HDD, I have never came upon such failure

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I'm not exactly new to the process either. That's one of the reasons I trusted my own actions and those of Disk Utility.

simsaladimbamba said:

Also know, that if "foo" is the first partition and "bar" is the second partition, deleting "foo" will not let you extend "bar", as one can only extend/shrink one partition via its end, not its start.

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In Disk Utility, you're right, there is no way to do this. Partition Magic had this function, as does some other programs, but not Disk Utility.

simsaladimbamba said:

Therefore deleting "bar" and extending "foo" would have worked quite well, unless you may have had a corrupted partition table. You could have simply used the ERASE tab with the "foo" partition and be done with it.

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If by this you mean I could have copied the files on "bar" to an intermediary directory, then deleted "bar", extended "foo" and copied them back to the new extended "foo," you're right, I could have done that. But the actions I did take theoretically should also have worked, and they didn't.

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Yahooligan said:

Out of curiosity, did you not change the partition table type from Master Boot Record to GUID when you initially formatted the drive? Unexpected things will happen when you mess with partitions on a drive set to MBR as it's not as flexible as GUID.

If you had used GUID then you should've had no problem resizing the remaining partition unless it wasn't the first partition, which it sounds like it wasn't. As the poster above says, you can't resize the beginning of the partition and extend backwards to the start of the disk, you can only extend the end of the partition.

Hope you had a recent backup and you're only out the time it takes to get it back the way you want.

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In all honesty, I don't remember what the partition map scheme was set to (it's GUID now) and it may well have been MBR. This could have been the problem, and I appreciate your insight. It would have been nice if Disk Utility had (1) been able to handle MBR-typed drives correctly, or (2) refused to commit changes at all, or (3) said something like "Whoa. You're trying to create a new partition on an MBR-typed drive. This will likely screw over your data. Are you sure you want to do this?"

As far as the backup goes, I'm pretty sure that at least some of the data wasn't backed up. What I was doing when this happened was consolidating my data with the intention to back it up. I'm in the process of recovering the files via various recovery software, and I think I should be able to get all of it back.

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Yahooligan said:

Unexpected things will happen when you mess with partitions on a drive set to MBR as it's not as flexible as GUID.

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I wanted to address this specifically. "Unexpected things" happening is exactly what a DISK UTILITY program shouldn't do and why I wanted to mention my situation in case others decided to try this.

blueroom said:

All the more reason everyone should have a backup solution.

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Yeah, well. I do have one, a time capsule. It won't fit all my data, because some of it is redundant, because of backup attempts of yesteryear. That's why I was consolidating my data which ironically caused this problem.