Re: Hot plugging of SATA disks doesn't seem to work under NetBSD-4.x?

[jnemeth%victoria.tc.ca@localhost (John Nemeth)]

On Jul 31, 11:02am, der Mouse wrote:
}
} > In general SCSI disks aren't hot pluggable unless they're hanging off
} > a hot pluggable bus such as Cardbus or PCMCIA (or inside a RAID
} > enclosure where the RAID controllers deals with drives coming and
} > going).
} 
} That does not match my experience.  Provided the bus is quiet at the
} time of connect/disconnect, I have never had any problem hot-plugging
} SCSI drives.  (Arranging for the bus to be quiet can be anywhere from
} trivial to almost impossible, depending.)
} 
} Of course, there may be softwre issues, such as (under NetBSD) a need
} to scsictl detach before hot-unplugging and scsictl scan after
} hot-plugging, but that's a separate issue.

     Not to mention problems with open files / filesystems.  It better
be unmounted before hot-unplugging.

} > Note that in general, hot plugging SCSI devices can do bad things.
} 
} Such as?  And, if it's not obvious from the answer, any guesses why
} I've never been bitten even though I've done it probably more than
} hundred times over the years I've been working with SCSI?

     I've done it a number of times too, but this definitely falls
under the heading of not recommended (as in the hardware isn't designed
for this).  I've even hot plugged internal drives and except for one
occassion (toasted the drive right before a show) didn't have any
problem.

     The biggest problem (as you mention above) is quiescing the bus.
Next is that since SCSI generally isn't designed for hot swapping, you
can cause spikes on the bus, which can crash the SCSI bus or in extreme
cases cause physical damage.  Similarly when connecting or
disconnecting power you can have spikes there that can cause physical
damage.

}-- End of excerpt from der Mouse