The sderaster update operation replaces a target raster with a source raster.
For example, consider the following ArcSDE command:
sderaster -o update -l myrasterdb,raster -f roads.tif
This replaces the raster dataset myrasterdb with roads.tif. The original pixel data of myrasterdb is removed before the replacement occurs.
The update operation should not be confused with the mosaic operation, which replaces that part of the target raster overlapped by the source raster.
sderaster -o mosaic -f myrasterdb,raster roads.tif
This command replaces only that part of myrasterdb that is overlapped by the pixels of roads.tif. Other pixel data of myrasterdb remains unchanged.