System Administration Guide: Devices and File Systems

Copying Data With the ufsdump Command

The ufsdump command copies data only from the raw disk slice. If the file system is still active, any data in memory buffers is probably not copied. The backup done by the ufsdump command does not copy free blocks, nor does it make an image of the disk slice. If symbolic links point to files on other slices, the link itself is copied.