I never felt the urge to try soft sectoring. Low level formatting ESDI drives need to be low level formatted before they are usable. So, first think, then format. The format time must not be underestimated, for big disks it can take hours. After a low level format, a surface scan is done to find and flag bad sectors.
Most disks have a manufacturer bad block list listed on a piece of paper or adhesive sticker.
In addition, on most disks the list is also written onto the disk. Please use the manufacturer's list. It is much easier to remap a defect now than after FreeBSD is installed. Stay away from low-level formatters that mark all sectors of a track as bad as soon as they find one bad sector. Translations Translations, although not exclusively a ESDI-only problem, might give you real trouble.