UDA50 and bad block forwarding

[David L. Gehrt]

There is a flag mentioned in the mscp header file in 4.2

#define	M_UF_REPLC 0100000 /* Controller initiated bad block replacement */

(sys/vax/mscp) which seems to imply that the controller will do bad
block on its own.  I don't know what that means.  VMS goes through a
very elaborate tap dance with the controller to accomplish "host
initiated bad block replacement."  The work done in this tap dance
implies that bad block reports (a bad block report is *not* just any
hard error, it is an end message flag with the M
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