The ufsdump command writes a sequence of fixed-size records. When the ufsdump command receives notification that a record was only partially written, it assumes that it has reached the physical end of the media. This method works for most devices. If a device is not able to notify the ufsdump command that only a partial record has been written, a media error occurs as the ufsdump command tries to write another record.
The ufsdump command automatically detects the end-of-media for most devices. Therefore, you do not usually need to use the -c, -d, -s, and -t options to perform multivolume backups.
You need to use the end-of-media options when the ufsdump command does not understand the way the device detects the end-of-media.
To ensure compatibility with the restore command, the size option can still force the ufsdump command to go to the next tape or diskette before reaching the end of the current tape or diskette.