I don't know if netbsd people have read this already, or found it for
themselves, but I found this comment interesting in a readme for a
solaris2-x86 driver disk udate:

NOTE 1:
        Our testing has uncovered a problem in the firmware used with
        the AHA-2940U, AHA-2940UW, and embedded HBAs that use the
        AIC-7880 controller chip (models of the Adaptec HBAs that
        use the AIC-7870 chip are not affected).  This firmware problem
        may occasionally cause the SCSI bus to hang in a state from
        which it can not be recovered without doing a hard reset,
        potentially corrupting data on your disks.  So far this problem
        has only occurred on test systems after several hours of very
        heavy I/O stress testing using multiple SCSI devices.  Because
        of the serious nature of this problem, an updated version of
        the adp driver will be provided as soon as this problem is fixed.