DB2: UNLOAD Vs Image copy

Difference between UNLOAD and image copy can be best explained using a table space which has compression enabled.

When the table space is compressed, the unload program has to first uncompress the table space and then extract the rows from each page. If you unload selected columns from a table, then DB2 has to selectively extract those columns from each page for each row.

But Image copy does not work that way. When we perform full image copy of the table space, the image copy utility simply copies the underlying LDS datasets to the output sequential datasets. It is just a plain copy and no uncompression is performed. The output sequential dataset will be exact replica of the underlying LDS dataset.