[ I've been having some email troubles
and have (apparently) lost messages both
inbound and outbound, so apologies if this
is a repeat, but I never saw my first post. ]
This same tantalizing idea has intrigued me on and
off for years: a PeeCee with some cheap IDE drives
and a SCSI controller in it is theoretically all you
need to make a RAID box. Unfortunately, I've always
been too busy with other things to get beyond the
"Wouldn't that be cool!" stage.
Two problems that come immediately to mind are
(A) getting your HBA+OS to act in the role of SCSI
target, and (B) performance. Solving A means you'd
have to think about interesting stuff like: what
should our HBA+OS do in response to a SCSI bus Reset?
A generic Linux-style solution to A will almost
certainly degrade B, while a customized solution to
A probably means you don't get to leverage as much
existing code as you'd like.
Meanwhile, solving B means obsessing about latencies/
throughput; doing all the RAID striping/mirroring
junk while absolutely minimizing the amount of time
you spend servicing interrupts, copying data, context
switching, etc...
>Can SCSI controllers talk to SCSI devices attached
>to DIFFERENT SCSI controllers?
I'm not sure I understand your question but if you're
asking whether multiple HBAs can be on the same cable,
then Yes, because SCSI devices aren't "attached"
to SCSI controllers - SCSI devices are all peers,
just like Enet devices. Using old-style SCSI (with
its 8 possible device IDs) as an example there's
nothing (technically) to prevent you from having the
HBAs from seven different computers all connected
to the same SCSI cable and talking to one single
(desperately overworked) disk.
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