I have a setup with Mac OS 10.8.5 on one drive, Windows 7 on a separate drive. This wasn't set up with boot camp, but installed directly. With Parallels 7, I couldn't seem to get it to boot from the separate drive, but Parallels 9 can run from it, which makes me happy. Unfortunately, Parallels 9 is very forgetful about it, too. I've run this from both MBR and GUID drives. Both exhibit the same behavior. In each case, there was the usual small "System Reserved" partition in addition to the rest. No problem. To get Parallels to boot from it, I needed to go to the drive configuration, select the Windows drive, click "Edit Partitions", and make sure both boxes were checked for each. Then it would boot. Yay! It runs wonderfully. However, seemingly at random, it will forget that I ever did that when I open Parallels again to run the VM. I'll try to run it and it'll tell me that it doesn't support this partition type or something to that effect. When I go back into the VM configuration, it shows my Windows drive as both disk0 AND disk1, duplicating it in the drop-down list, which is ridiculous as disk1 is, according to the system, my Mac OS drive (which is, granted, a Fusion drive created through the Terminal, but I doubt that's the issue here). Both drives appear in the configuration, but only one of them will allow me to edit partitions and check the box again to make sure the Windows drive is included. Once I do select this, the duplicate drive disappears from the drop-down list. When I try to start up again, it'll throw another error saying that it can't unmount the drive. Try again and it runs...and reinstalls Parallels Tools. Lovely. I have to wait for that to finish. When it does, everything runs fine (I don't need to reactivate Windows, thankfully), but it's bound to happen again after a few launches. What gives? How is that Parallels is getting mixed up about this drive and thinking it's in two places, then somehow thinking that Parallels Tools isn't installed?
Yes, Boot Camp partition support in Parallels is not as smart as it could be. If you see the drive listed twice in the menu with different disk numbers (like disk0 and disk1) then it probably means that the disk number of the drive has changed since the time Parallels set the hard drive preference of your virtual machine. The first occurrence of the drive in the list shows the current disk number. The second occurrence shows the old disk number. Using the disk number is bad since it's not guaranteed to be the same across reboots even for internal drives. There's a bunch of identifying information Parallels Desktop could use instead (GUID partition IDs, NTFS or FAT or whatever file system UUIDs, MBR drive serial number, start block, size, etc). I believe I've had Parallels boot VMs without problem with no user intervention when the disk number has changed so I think it's using some of the other identifying info in that case. I do not doubt that it might occasionally not work though. Parallels shows the model name of the drive like Disk Utility does but that won't be unique if you have more than one of the same model. When you change the drive setting, Parallels will unnecessarily unmount and check the partition and then remount the partition. Trying to boot the virtual machine during this time consuming and annoying process will cause an error so you just have to wait until you see the partition on the desktop again. I don't think there's any good reason for Parallels to be unmounting the partition at this time. If what it's doing is important, then Parallels can do it later when the virtual machine is starting. When you start the virtual machine, Parallels will unmount the partition so that the virtual machine can use it. Changing the Boot Camp drive setting for a virtual machine causes Parallels to set some kind of "Parallels Tools needs installing" flag which is annoying if you know Parallels Tools is already installed on the selected drive. There should be an option to disable this, or Parallels should be smart enough to know that Parallels Tools does not need reinstalling. Since Parallels Tools is installed, the Parallels Tools drivers will load in Windows, and the drivers can tell Parallels Desktop that it doesn't need installing. Other Parallels Boot Camp disk issues: It should allow selecting non-Windows partitions (Mac OS X, etc) for the Boot Camp option. Since all attached partitions are visible to all any OS you boot on the Mac, there is no reason to hide them from any OS you can boot in Parallels. It should allow changing the active partition setting in the MBR. Basically, when you're using the Boot Camp option in Parallels, you are constructing a virtual disk for the virtual machine. When you select partitions, you are telling Parallels that those parts of the virtual disk will be read from the actual disk. An important piece of a disk is the MBR. Parallels creates a copy of the actual disk's MBR for the virtual disk. Whatever partition that is meant to be booted is set in the MBR. This might be the System Reserved Partition which is why you have to make sure it's one of the selected partitions. You might have a disk with multiple partitions, each with there own boot code (for example, a disk containing Windows XP, Windows 7, and Linux). You might use a boot loader on your Mac that can boot any of those partitions. For Parallels, you would want to create a virtual machine for each partition, each would have there own Boot Camp virtual disk, but you would need to edit the virtual MBR of each virtual disk to point to the proper partition. This would be easier if Parallels had an option to set the active partition in the MBR.
