[...wide and narrow on the same bus...]
If you
do it right, [...]
If wide SCSI devices are on high IDs, won't they be unable
to
communicate with narrow devices on the same bus?
Yes. But I know of very few systems that actually take advantage of
the way devices other than the host can act as initiators. (For that
matter, the phrasing "the host" betrays an assumption that there is
only one host on the bus, another thing that is not safe to assume in
theory but is almost always safe to assume in practice.)
So, as long as the host is wide....
The coolest example of non-host initiators I recall seeing came from
reading over the command set of some particular disk drive. It had a
command which made it act as initiator and perform reads from other
devices, XORing the resulting data together and writing the result to
its own media. (I assume this was intended to allow RAID rebuilds to
avoid passing everything through the host.)
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