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Date:      Tue, 18 Jul 2000 10:46:59 -0400 (EDT)
From:      Mikhail Teterin <mi@privatelabs.com>
To:        scsi@freebsd.org
Subject:   slow tape behind fast drives on the chain
Message-ID:  <200007181446.KAA76520@misha.privatelabs.com>

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Hello!

For a while we were happy with two external 45Gb drives hanging off
of AdvanSys 3550 Ultra SCSI Adapter:

da0 at adw0 bus 0 target 2 lun 0
da0: <SEAGATE ST446452W 0001> Fixed Direct Access SCSI-2 device 
da0: Serial Number LF214132
da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit), Tagged Queueing Enabled
da0: 44884MB (91923356 512 byte sectors: 255H 63S/T 5721C)
da1 at adw0 bus 0 target 3 lun 0
da1: <SEAGATE ST446452W 0001> Fixed Direct Access SCSI-2 device 
da1: Serial Number LF214978
da1: 40.000MB/s transfers (20.000MHz, offset 8, 16bit), Tagged Queueing Enabled
da1: 44884MB (91923356 512 byte sectors: 255H 63S/T 5721C)

Yesterday, we added the tape drive:

	pass2: <ARCHIVE Python 04106-XXX 735B> Removable Seq
	pass2: Serial Number GS0D9S5
	pass2: 3.300MB/s transfers

and the drives started to give all sorts of problems. This sounds like a
bad cable/terminator, but I wonder  if the combination is even suppoused
to work -- the tape has the Tectronix connectors on the back, the drives
have the 68pin. The short 68pin cables  connect one of the drives to the
adapter and to the second drive  which used to have an active terminator
on it's second  68pin jack. Now, there is a  68-50 cable there extending
the chain to the tape, which has an active terminator.

Would  access  to the  drives  be  slower  because  of the  tape's  mere
presense?  Will  it  slow  (noticable)  when the  tape  is  in  use?  It
everything should work fine (it does not)  -- what do I replace first --
the 68-50  cable connecting the tape  to the second drive  or the active
terminator on the tape?

Thanks a lot!

	-mi


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