Write data rate twice that of read rate?
 

When using SuperDuper to backup to a sparse file on a local Firewire disk I noticed that the data write rate as observed by Activity Monitor is twice the data read activity. When copying files using other programs, e.g. Finder, the write rate is the same as the read rate.

Why is SuperDuper writing twice as much as needed?

Perhaps you're seeing us writing to the image, and the image writing itself to the drive? We definitely don't copy the data twice... in fact, the actual file copy is done with a single system-provided API which we then supplement with additional metadata (though not primary data) copies.

That must be it. Thanks.