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List:       netbsd-tech-kern
Subject:    Re: How to hot swap an SCA SCSI disk with NetBSD
From:       Mouse <mouse () Rodents-Montreal ! ORG>
Date:       2013-10-27 15:34:17
Message-ID: 201310271534.LAA09806 () Chip ! Rodents-Montreal ! ORG
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>> 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).
> That's true, but, generally, SCA backplanes are intelligent devices
> which can report device insertion/removal to the host over the SCSI
> bus - see ses(4).

The backplane still has to notice it somehow.

Also, "generally" is, I suspect, an artifact of the hardware you've
worked with.  Most of my SCA equipment is not that smart - the SS20,
for example, uses SCA but has nothing of the sort as far as I can tell.

To get back on the original subthread, I wouldn't want to connect or
disconnect a load from a bus that's got live operations going on it;
for hot-swap, I'd expect switching electronics that does the
disconnect/reconnect before/after the electrical contact is
broken/made, and timed to not disrupt a transfer in progress.  Either
that or I'd use bidirectional buffer logic, so there is nothing like a
direct electrical connection between the SCA pins and the SCSI bus.

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