SUMMARY - SCSI-1 & SCSI-2 devices on same bus

From: Paul Kiesel (
Date: Thu Jun 23 1994 - 13:00:48 CDT

             SCSI-1 and SCSI-2 devices on the same bus
Original Posting :
> We are having problems with SCSI errors on our SS10/40. I have a 'white
> paper' dated October 21, 1992 from Sun with the title 'SCSI
> Configurations using Single-Ended Fast SCSI Devices'.
> Our Sun SE told us we can't mix SCSI-1 and SCSI-2 devices on a single
> chain. Period. I am asking him to give us more info and am looking
> into this independently.
> Our current system, an IPC, uses SCSI-1 external devices.
> We have moved the SCSI-1 devices from the IPC to the SS10/40.
> The SS10/40 also has an internal 1.05 Gig SUN disk
> which is a SCSI-2 device. Hence the first device in the chain is
> a SCSI-2 device the others are SCSI-1 devices (two disks, two HP
> DATS, one 150mb QIC tape).
> One of the old disks gave us fits with timing errors, the others
> appear to be stable, but I don't want to ignore a potential problem.
> Also, if only SCSI-2 devices are supported is there a way we can
> use our existing DAT and QIC tapes which are SCSI-1 devices?

Responses to Posting :
        1. Modify kernel to use asychronous SCSI only
                in /sys/scsi/conf/scsi_confdata.c comment out
                Major disadvantage is all devices on the bus will be at
        2. Install second bus card of type SCSI-1
                For $300 to $700 this may be a very reasonable option
        3. Keep bus length under 2 meters (6.65 feet)
        4. Use an active terminator
                If SCSI-2 Then
                  use active terminator
                elseif SCSI-1
                  passive termniation is OK
        5. First SCSI device may not be a SCSI-2 device
                make first device a SCSI-1 device and the interface will
                will sync on it (5mb/sec) and assume all devices on the
                bus are 5mb/sec (SCSI-1). The effect being not unlike
                number 1 above.
        6. SCSI-1 is OK on a SCSI-2 bus along as the SCSI-1 devices support
           SCSI-2 signalling. (The SCSI controller will negotiate transfer
           rate with each device individually.)
        7. SCSI-1 and SCSI-2 cannot be mixed on the same bus
        8. Do not use cables with 3rowfiftypin connectors, they do not
           conform to SCSI-2 specs

As can be seen the responses were varied. Our SUN SE confirmed, along with
others, an active terminator must be used. We have not tried Number 1, but in
our application it may be possiblity and will require some testing.
Number 2 is a strong contender as a solution.
Numerous responses indicated that there was no danger of data corruption, as the
errors are soft errors, but the system takes a performance hit when its dealing
with the SCSI bus errors, and this is definitly noticable.
Our system is stable as it stands, we have made no changes as of yet.
SCSI errors only occur when we try to run an Informix archive to one
of the HP DATs on the system. Informix uses dd for archiving. (We have run dd
from the command line to the same tape unit with no problem. ???)

Some good references for further reading
SCSI FAQ (from some ftp site which now escapes me
                 for those wanting a copy drop me a line
                 and I'll send it out)
SUN White Paper - SCSI Configurations using Single-Ended FAST SCSI
                 (for those wanting a copy drop me a line
                 and I'll send it out)
SCSI Standards / Specifications - Available as part of the
                 scsiinfo / scsiping utility set available from
                 numerous ftp sites (well worth having utilites)
                 (Careful on this one - hardcopy is 4" thick single-sided)

General Info
Sun Sparc 10 systems use SCSI-2 interfaces with transfer rates of
10mb/sec. The output of scsiinfo indicates this is the speed value
for device sd0. (If the controller only supported SCSI-1, the transfer
rate would show as 5.0mb/sec.)
        SCSI Interface Logical Device SCSI SCSI Interface
        Interface Name Device Name Address Number
        ~~~~~~~~~~~~~~ ~~~~~~~~~~~ ~~~~~~~ ~~~~~~
        esp0: st2 tgt 1 lun 0:
                Asynchronous Clean CanReconnect
        esp0: st1 tgt 5 lun 0:
                Synchronous(5.0MB/sec) Clean CanReconnect
        esp0: st0 tgt 4 lun 0:
                Synchronous(5.0MB/sec) Clean CanReconnect
        esp0: sd3 tgt 0 lun 0:
                Synchronous(4.445MB/sec) Clean CanReconnect
        esp0: sd2 tgt 2 lun 0:
                Synchronous(5.0MB/sec) Clean CanReconnect
 -----> esp0: sd0 tgt 3 lun 0:
                Synchronous(10.0MB/sec) Clean CanReconnect
As does the output of scsiping
            Capacity: 2059140
            Peripheral qualifier: 0 currently connected
            Peripheral device-type: 0 direct
            Device-type modifier: 0
            Removable medium: No
            ISO version: 0
            ECMA version: 0
   -------> ANSI version: 2
            Async event notific. No
            Term.i/o process msg: No
   -------> Response data format: 2 (SCSI-2)
            Relative addressing: No
            Wide bus 32: No
            Wide bus 16: No
            Sync transfer: Yes
            Linked commands: No
            Command queing: Yes
            Soft reset: No

Paul Kiesel
CADD /CAE - Information Systems
Raytheon Engineers & Constructors
Phila, Pa, USA
Voice 215-422-3598 FAX 215-422-3800
E-Mail :

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