1. A method in a data storage subsystem of updating SMD in storage devices 1 -N, wherein a set of the SMD copies written on storage devices 1 -N define a copy set X, comprising: (a) receiving an SMD update request and updated SMD; (b) changing the start tag values of a copy set X; (c) writing the updated SMD of copy set X; (d) changing the end tag values of copy set X; (e) changing the value of X; and (f) repeating steps (b) through (e) at least once.