why mysql-utilities sepeate filed to normal and blob,and mysqldbcopy very slow when the field is text (no replies)

when I mysqldbcopy a table contain 20w rows and one field's type is text.
mysqldbcopy will insert the data at first,it's very fast, only use 1 minute，
After that, It will spent 40 minutes to Update the 20w again for the text field.
So it's some way to fast the performance?