tape changer, but not tape drive

[Adam McDougall]

On Tue, Oct 27, 2009 at 09:39:07PM -0400, Dan Langille wrote:

  I first encountered this problem in April, now I'm back to it:
  
     http://lists.freebsd.org/pipermail/freebsd-scsi/2008-April/003452.html
  
  In short, the system has tape library.  The library has worked in the 
  past (http://www.freebsddiary.org/digital-tl891.php) but now it does 
  not.  I can see either the tape library or the tape drive.  Which I see 
  depends upon the cable configuration.
  
     http://www.freebsddiary.org/images/tape-libraries-cables.jpg
  
  As shown above, that's how I would expect things to work normally. 
  However, in that configuration, I do not see the tape drive.  The cable 
  going down, goes to the computer.  If I reconnect that cable to the plug 
  to the left of the terminator, the system can see the DLT drive, but not 
  the tape library.
  
  Under 6.3-STABLE FreeBSD, I can see either one device or the other.
  
  ch0 at ahc0 bus 0 target 0 lun 0
  ch0:  Removable Changer SCSI-2 device
  ch0: 20.000MB/s transfers (10.000MHz, offset 8, 16bit)
  ch0: 10 slots, 1 drive, 1 picker, 0 portals
  
  or
  
  sa0 at ahc0 bus 0 target 1 lun 0
  sa0:  Removable Sequential Access SCSI-2 device
  sa0: 20.000MB/s transfers (10.000MHz, offset 8, 16bit)
  acd0: FAILURE - INQUIRY ILLEGAL REQUEST asc=0x24 ascq=0x00 sks=0x40 0x00 
  0x01
  
  Any ideas?
  
  Full dmesg output here:  http://www.langille.org/tmp/dmesg.boot
  
  TIA.
  
Is it possible the middle cable is broken in some way?  Perhaps you
could swap it with another cable to try to find out, such as with
the cable going from the library to the 2944 card.  Might be intermittant
and start working if bent or moved.  Also can you see the connectors
inside the library (on the back side of the external plate) to check
if they are well seated or damaged?  You could also try swapping the
first and second connection or the third and fourth, or both, if it is
hooked up like I think it is, those should have an equal chance of working
and might reveal a bad port or partially bad port.  Also try leaving off
the terminator or one/both ends of the middle cable just to see if the
system can tell the difference especially while booting, just to confirm
if it makes any negative difference at all.