Re: How to hot swap an SCA SCSI disk with NetBSD

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Oct 25,  2:20pm, Mouse wrote:
}
} > Generally speaking, SCA SCSI drives are hot-swap capable.
} 
} Sure...but the drive bays aren't necessarily.  For example, the drive
} bay in a SS20 probably isn't; you can't even get to it without removing
} the lid, so there'd've been little reason for Sun to spend the money
} for the signal switching hardware to make it hotswap.
} 
} > I'm not interested in fiddling with 50-pin or 68-pin with a paused machine 
-$
} 
} Actually, with a _paused_ machine, IME - I M limited E - it's fine.
} It's doing so on an active SCSI bus, one with transfers going on, that
} I was saying was a recipe for trouble.

     With SCA, or anything else that is designed for hotswap, the
ground pins are longer then the other pins.  This means that ground
disconnects last and connects first.  This prevents spikes.
Hotswapping with connectors that aren't designed for it can cause
physical damage to equipment, and thus is not generally recommended.

} > The key thing in documentation is not just how, but why.
} 
} > For example, why "scsictl <dev> detach"?  Why not just "stop" and
} > remove?
} 
} Personally?  The reasons which occur to me offhand:

     SCA is just a type of connector.  As far as I know, there are
no extra signals (in particular there is no way to signal the OS
that the device was removed).

} Because doing that doesn't get the teardown and rebuild I mentioned
} upthread.  Because not all the scsictl versions I have in use support
} stop.  Beacuse I'm not always replacing it with an identical drive (or,
} sometimes, at all).
} 
} > The idea here is to document a procedure generally. Odds are good lots of 
it$
} 
} Yeah - everything but the physical-layer stuff, I'd guess.
} 
} (SAS, gaaaah....)
} 
}-- End of excerpt from Mouse