WARNING: Boot Camp Assistant can reformat wrong drive

This is a notification to users of a bug in Mac OS X Lion. On Macs that do not have internal optical drives (Mac Mini or MacBook Air), the Boot Camp Assistant 4.0.1 can potentially reformat the wrong external storage device in a case where the user has multiple external volumes, when creating the Windows Installer from a Windows 7 .ISO disk image file. (In my case the disk image was on an external drive that Boot Camp Assistant reformated due to this bug.)

This is how I produced this issue:

I have a friend's brand new Mac Mini 2011 with 10.7.1. I wanted to create a Boot Camp parition, so I started Boot Camp Assistant.

On the Mac Mini the Boot Camp Assistant gives you three options: (1) Create a bootable USB volume, (2) Download and burn the Apple drivers to CD/DVD, and (3) Install Windows on your Boot Camp Partition. Option (1) is new to Lion as mentioned by Apple here:

• Support for the Windows 7 ISO installer
• Install Windows with an installation disc you provide or, on Mac computers that do not have an optical drive, with a USB flash drive that contains a Windows 7 ISO image downloaded from Microsoft. The Boot Camp Assistant will offer to create this image on supported computers.

Apple's website does not say that you MUST install from a USB drive and not a DVD, and the Boot Camp Assistant screen does not say you can't either. Since I have an external LaCie DVD-RAM drive, I figured that I should just install Windows the old fashioned way -- from the DVD.

So, I unchecked Option (1) and used Boot Camp Assistant to create a new partition on the internal drive, on which to install Windows 7. The partition itself was successfully created on the internal hard drive of the Mac Mini. I burned the Apple drivers to CD using an external USB LaCie DVD-RAM drive. Next I inserted the Windows 7 disk into the external DVD drive, and pressed Continue to restart the Mac and install Windows. However the computer just showed a green screen with the text saying basically, "No bootable volume found."

At this point I don't know why it would not boot up from the Windows 7 disc that was in the DVD-RAM drive, since that disc worked fine on my Mac Pro for creating the Boot Camp partition, and evidently it is OK with installing from a USB stick. I even tried my friend's Windows 7 disc that he had brought, which was the same version, but it also failed.

So after hard-restarting the Mini, we got the ISO file and a 16GB USB stick and proceeded to try it the other way. The ISO file had been downloaded onto a USB hard drive that had two partitions: an HFS+ partition and a FAT-32 partition. They were called "Velcro" and "Velcro DOS." We used my Mac Pro to copy the ISO file onto that USB hard drive, then attached that drive to the Mac Mini along with the 16GB USB stick that was called "SIXTELN."

We opened Boot Camp Assistant and checked all three options. It asks you to select the Windows 7 ISO file, and I did select it on my external volume called "Velcro." Then it asks to choose which device to create the installation partition on. I selected "SIXTELN" to reformat and made sure that was the correct volume when it reminded me that I would lose all my data. So I hit "Continue" and then what happened next is that it formatted the wrong drive.

Boot Camp Assistant creates a volume called WININSTALL from which the Mac will boot, and from which Windows will be installed.

Let me resummarize for those of you who cannot accept the fact that this could actually be possible.

I attached my USB hard disk which two partitions, one Mac HFS+ and the other FAT 32 (entitled "Velcro" and "VelcroWin" respectively). Then I inserted the USB stick, a 16GB SanDisk Cruzer called "SIXTELN." The Mac HFS+ volume "Velcro" contained the Windows 7 ISO file, which I selected in Boot Camp Assistant to use for creating the startup USB disk. Next, I selected the USB stick "SIXTELN" as the device to reformat and use for creating the bootable Windows 7 installer. I then double-checked that I had selected the correct device, and even "SIXTELN" in the Finder to make sure there were no files on it that I couldn't stand losing. I clicked Continue to proceed, and was presented with a warning that "SIXTELN" would be erased and all its files deleted. I pressed "continue" and then I was confounded as the WININSTALL volume that was created showed 322 GB available, and an error message appeared in Boot Camp Assistant saying that it could not continue.

That was when I realized the truth:

Boot Camp Assistant had erased the entire USB hard disk including both both partitions, one of which contained the Windows 7 ISO file that I had selected to install from! The installation could not complete because it could not find the Windows 7 ISO file anymore! The software never warned me it was going to erase the Volume entitled "Velcro" nor "VelcroWin". It shouldn't have done so anyway, since the ISO file was on "Velcro"!

Software should never delete a file it is planning to read from, then try to read from it. Ever. For example, Disk Utility will not allow you to reformat your startup volume, because it's impossible, since Disk Utility depends on files that are on the startup volume! Boot Camp Assistant should not ever reformat the volume containing the Windows ISO file that has been selected to install from.

I suspect an error in the code of Boot Camp Assistant (like using the wrong variable) resulted in the software formatting the wrong drive. I'm certain, because I had named the volume for installation, "SIXTEEN" and when I selected it, I switched to the finder to open it and look at its contents, then switched back. Then it said basically, "Are you sure you want to reformat the volume, SIXTEEN, which will delete all its contents?" And I said yes to this.

From what I have read on these forums today, many people have had many problems trying to install Windows 7 onto MacBook Airs and Mac Minis due to their lack of DVD drives. There are a ton of bugs in Boot Camp Assistant and this whole process is confusing and not clearly documented. Personally with all due respect, in the case of MacBook Airs then I can understand the omission of a DVD drive. But in the case of Mac Mini, I cannot understand it at all. Macs are supposed to be simple to use; read this other thread and witness the complexity that users have had to go through just to get Boot Camp running on a MacBook Air or Mac Mini.

Further I cannot understand why Apple makes Macs that require booting from a USB stick to install Windows 7, but that do not allow users to simply install from an external USB DVD drive. If you're going to remove the DVD drive from the computer then at least give users an alternative solution that is not buggy.

EDIT: fixed some typos.

EDIT 2: see this thread about how to properly install Windows 7 on Lion if you have a Mac Mini or MacBook Air without the optical drive, without a DVD drive. An external DVD drive will not work.