MPS driver: force bus rescan after remove SAS cable

Jeremy Chadwick freebsd at
Wed Apr 27 12:57:41 UTC 2011

On Wed, Apr 27, 2011 at 02:20:34PM +0200, Denny Schierz wrote:
> hi,
> if I remove the SAS cable from the JBOD (connected through a SAS
> switch), all disks disappears, that's fine and expected, but if I
> reconnect the cable, the disks are not added anymore.
> I've red to use "camcontrol rescan all", but nothing happens. I don't
> get my /dev/da0-47 devices anymore and have to reboot the whole machine.
> What is my mistake?

Does resetting the bus then rescanning improve things at all?  E.g. for
bus 0 (use "all" only if it's safe):

camcontrol reset 0
camcontrol rescan 0

I'm doubting it will.  This is the first time I've heard of something
called a SAS switch (looks like a SAS expander to me), but searching the
Web indicates that most of these devices have a form of
firmware/administrative interface on them, which means it's highly
likely that the device itself is "getting in the way".  Meaning: what's
to say the issue is with FreeBSD and not with the SAS switch?  To me, my
first choice of action would be to contact the device vendor and ask
what the behaviour should be.

If there's some sort of device with an ASIC in between your disks and
the controller (which is the case here), that could be responsible for
what you're seeing.  Or, if the hot-swap backplane has something like
SES (not a typo) or a QLogic GEM chip on it, that could be causing some
issues.  (In the case of the latter on our SCSI systems at work, we
change the physical SCSI cabling in our systems to remove the GEM from
the bus entirely, otherwise it does odd things like tries to renumber
the SCSI IDs on devices during a failure, and more often than not locks
the entire SCSI controller up).

Bottom line: less actual stuff between the disk and the controller the
better.  :-)

| Jeremy Chadwick                                   jdc at |
| Parodius Networking              |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.               PGP 4BD6C0CB |

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