While experimenting with TimeMachine’s unsupported network backup capabilities I rsync’d my host_blah.sparsebundle from one drive to another (without using -E, more on that later). The result was that my .sparsebundle now appeared in the Finder just as a normal folder, instead of with a disk image icon. This also meant that I couldn’t open the image in DiskUtility any more.

The fix is to use SetFile to restore the “Bundle” attribute.

$ /Developer/Tools/SetFile -a B host_blah.sparsebundle

The first time I mounted it afterwards I had to wait for fsck_hfs to complete, since the “com.apple.diskimages.fsck” attribute had been cleared, but otherwise it’s back to it’s old self.

I also learned that in order to avoid this (and many other much nastier problems) you should use the -E flag for rsync under Mac OS. This correctly copies over the resource forks, extended attributes and meta-data also.

(This item is probably old-hat to many Mac users, since Bundles have been in the Finder since OS 9. But it took me a couple of days of searching and experimentation, so I figure it could use some better visibility.)