Norton Speed Disk and leaving data fragments in the extent data: Alsoft re-replies

It started with a reader report of an error message by DiskWarrior that seemed to occur only after running Norton Utilities' Speed Disk. Alsoft offered an explanation. Symantec had a different view. Today, Alsoft offers a rebuttal. I expect this to be end of this matter on MacFixIt (Alsoft and Symantec are now working together to resolve this issue among themselves). Alsoft 's Joe Muscara writes:

Fact 1: When the Mac OS creates the catalog or extents trees, the unused portions (nodes) are cleared with zeros.

Fact 2: When the Mac OS grows the catalog or extents tree, the newly allocated fragments of the trees are cleared with zeros. Fact 3: When enough extent data is removed from the extents tree to free a node of the extents tree, the Mac OS clears that node with zeros before freeing it.

The reason that these unused nodes are cleared by the Mac OS is to aid the task of a directory repair program when scavenging a damaged directory.

After completely defragmenting a disk, all nodes in the extent tree are free, and therefore all should be cleared to zero to conform with the behavior of the Mac OS. Free nodes that contain extent data are the source of the message from DiskWarrior.

Furthermore, leaving extent data after defragmenting a disk is of no value to any recovery program because it points to locations where files used to be before being defragmented and not where they are currently located. In fact, because disk optimization programs pack files together, it is almost a certainty that a file's old location has been overwritten by another file. Therefore there is no benefit to leaving old data in the extents tree.