The new version of Parallels is out. I bought it, downloaded it, and installed it. They've changed the virtual machine format so you have to convert them. The slowest part of this process was making a backup (my Windows Vista VM is over 100 gb).
Everything worked fine, and I should have left well enough alone, but during the upgrade process I noticed that my 30 gb virtual disk file was 80 gb. So I thought I'd try the Compressor tool. (I'd never used it before.)
I got this message:
Parallels Compressor is unable to compress the virtual disk files,
because the virtual machine has snapshots, or its disks are either
plain disks or undo disks. If you want to compress the virtual disk
file(s), delete all snapshots using Snapshot Manager and/or disable
undo disks in the Configuration Editor.
So I opened the Snapshot Manager and started deleting. I deleted the most recent one, but when I tried to delete the next one it froze. I waited a while, but nothing seemed to be happening and the first deletion had been quick. I ended up force quitting Parallels, although I hated doing this when my virtual machine was running since that's caused problems in the past.
But when I restarted Parallels it was still "stuck". Most of the menu options were grayed out. When I tried to quit I got:
Cannot close the virtual machine window.
The operation of deleting a virtual machine snapshot is currently in
progress. Wait until it is complete and try again.
I force quit Parallels again. I tried deleting the snapshot files but that didn't help. Force quit again.
I had, thankfully, backed up the upgraded vm before these problems. But it took an hour or more to copy the 100 gb to or from my Time Capsule. (That seems slow for a hardwired network connection, but I guess it is a lot of data.) So first I tried to restore just some of the smaller files, figuring the big disk images were probably ok. This didn't help.
Next I tried deleting the Parallels directory from my Library directory, thinking that might be where it had stored the fact that it was trying to delete a snapshot. This didn't help either.
So I bit the bullet and copied the entire vm from the backup. An hour later I start Parallels again, only to find nothing has changed - same problem. Where the heck is the problem?
The only other thing I can think of is the application itself so I start reinstalling. Part way through I get a message to please quit the Parallels virtual machine. But it's not running??? I look at the running processes and sure enough there's a Parallels process. Argh!
In hindsight, the message that "an operation" was "in progress" should have been enough of a clue. But I just assumed that force quitting the application would kill all of its processes. I'm not sure why it didn't. Maybe Parallels "detached" this process for some reason? I also jumped to the (incorrect) conclusion that there was a "flag" set somewhere that was making it think the operation was in progress.
If this had been on Windows, one of the first things I would have tried is rebooting, which would have fixed this. But I'm not used to having to do that on OS X. I probably didn't need to reboot this time either, killing the leftover process likely would have been sufficient. But just to be safe I did.
Sure enough, that solved the problem, albeit after wasting several hours. Once more, now that everything was functional, I should have left well enough alone, but I can be stubborn and I still had that oversize disk image.
This time I shut down the virtual machine before using the Snapshot Manager and I had no problems deleting the snapshots.
But when I restart the vm and run Compressor, I get exactly the same message. I have no snapshots, and "undo disks" is disabled. I'm not sure what "plain" disks are, but mine are "expandable" (which is actually a misleading name since they have a fixed maximum size) and the help says I should be able to compress expandable drives. I have no idea why it refuses to work.
While I'm in the help I see you can also compress drives with the Image Tools so I try that and finally I have success. My disk image file is now down to 30 gb. I'm not sure it was worth the stress though!