The inability to have a cancelled process immediately terminate may be
an architectural choice where it is desired that TSM's behavior be
uniform across platforms and devices, so as to have uniform
documentation et al.  While it may be straightforward for a TSM module
to terminate a TSM server I/O process in a limited set of
circumstances, it might not be possible in other circumstances; and
the programming to achieve it in one arena may be very different than
in another.  Then there is all the complexity of undoing the
incomplete operation without losing any information, or duplicating
any - which gets hairier as I/O becomes more dissociated, as with
SAN.  The developers probably looked into this in the past and decided
to avoid putting their foot into it.

   Richard Sims