The last couple of days have provided several reminders of why the tag line for this blog is “A Frustrating Journey” and Superduper! was one of them. Superduper! is Mac disk cloning software that I wrote about recently and use for my backups. Since writing that I’ve had a couple of problems with Superduper!, the most recent occurred at the same time as I was dealing with my IE problems so it took me awhile to look into it.
The first occurrence was a little over a week ago when the backup failed with an error that said the disk was full. As these things usually occur at the worst time I just quickly looked and saw that I was backing up 160GB to a drive with 290GB of available space so it would fit. The destination image file did fill the 300GB drive so it was a valid error. I just deleted the file and started a full backup while I headed off to work. It was fine when I got home.
The next issue was a couple of days later when the backup failed because it couldn’t copy the extended attributes of an iTunes file. It looked like the file was probably being downloaded as Superduper! was running which could explain the error. But it’s still a bad thing that the backup failed at that point rather than displaying an error and move on.
Then the out of disk space error occurred again Thursday night. This time I decided to leave it until I had some time to look into it. The Superduper! website and forums don’t mention it so it was time to do my own research. To recap, I user Superduper! to back up my user directory to a sparse image file.
I mount the disk image and look at the properties in Pathfinder. It shows 0 bytes free. What’s a bit strange is that it shows a capacity of 465GB yet the drive it’s on is a 300GB drive. So it appears the Superduper! error is valid since Pathfinder also reports no free space. Then I fired up Disk Inventory X to see what files were taking up all that space. Well, the contents totaled 168.4GB, even when using the setting to use the physical file size on disk, not the logical size that’s reported by the file. I also used WhatSize to confirm the file usage was correct. WhatSize also reports 168GB used.
The Apple support knowledge base doesn’t provide any clues either. The only problems even close all involve FileVault which I’ve never used. So I fire up OS X’s Disk Utility to see what is says about the image file. It also sees it as a file with a capacity of 465GB with nothing available. I ran Disk Utility’s verify command on the image file and it passed. I wasn’t aware the verify command would actually change anything, but now Disk Utility says that 169.1GB is used (which is what I’d expect) and 296.4GB free. Sure enough, finder shows the same info.
I’m thinking the problem is with the Sparse Image file, or with the way Superduper! updates it. The image file does in fact fill the hard disk, but it’s just much bigger than it needs to be. Maybe the way Superduper does it smart updating causes poor handling of the free space in the Sparse Image file.
My choice of using an image file was a reluctant one, but at the time I couldn’t dedicate the external drive to the Superduper! backup. Now I can dedicate the drive to the backup so there’s a change in plans. I’ll clone the entire drive to the external and make it bootable. This has the benefit of being able to quickly recover from a drive failure. There will be a problem down the road though since my iMac hard drive is 500GB and the external is 300GB. I’m only using about 200GB now, so it should work until I upgrade. Or, I can go back to just backing up user files.