Unknown Source of SCSI Bus Errors (fwd)

[Andy Smith]

Hi,

I sent the message below to the aic7xxx mailing list last week with 
no reply. Since then I have made more progress on understanding
the problem, however I have no solution. The more I look, the 
more I am convinced that the problem is in software. For starters,
I have updated my aic7xxx module to the latest version (5.1.26).
This changed in no way the behavior of the computer. Then I went
through each of the switches in the SCSI Select BIOS utility. I switched 
things that are by default disabled to enabled and vice versa. I 
found that if I turn off "Initiate Sync Negotiation", the SCSI
bus and the disks work: No SCSI errors! The problems is that the
disks are accessed in asynchronous mode at 20MB/s. As the mode is
asynchronous, the actual speed of the disks is more like 10MB/s.
(dd if=bigfile of=/dev/null bs=10000). Pretty pitiful for an 
ultra-wide bus connected to an array of ultra2 disks. 
The problem seems to be with synchronous data transfers, not termination
as I suspected before. 

Any help?

-Andy


---------- Forwarded message ----------
Date: Mon, 14 Feb 2000 09:25:37 -0500 (EST)
From: Andy Smith <asmith at umdgrb.umd.edu>
To: aic7xxx at FreeBSD.ORG
Subject: Unknown Source of SCSI Bus Errors


Hi,

I have a problem which seems to be closely linked to the aic7xxx
driver. I have a Dell Precision 410 with 2 500 MHz cpus running the
smp version of the redhat 6.1 kernel (2.2.12-20smp). The motherboard
has 2 imbeded scsi hosts, an AIC-7890/1 Ultra2 Controller and a 
AIC-7880 Ultra SCSI Controller. In Addition I have added an 
AHA-2940UW. Attached to the system I have an array of 8 SCSI 
disks the disks themselves are Ultra2 (SEAGATE Model: ST150176LC), 
but the enclosure only supports
ultra-wide access. When I plug the array into the motherboard's 
AIC-7890 adaptor the disks are detected as "SE" devices and I can
access them to my hearts delight at 40Mb/s. When the same disk array is 
attached to the card based AHA-2940UW controller or to a AHA-2940U2W
controller that I have arround the office, continuous SCSI bus errors
make the drives unusable. For a long time to assumed that the problem
was due to hardware, but the problem is idendentical with the 
UW and U2W controllers. Then I thought that the prbolem might 
be due to a poor connection or cable, but I can use the SCSI Select
BIOS configuration utility to "verify" the contents of the disk without
errors. Finally I noticed the following in my /var/log/messages file:

 (scsi0) <Adaptec AHA-294X Ultra SCSI host found at PCI 14/0 
 (scsi0) Wide Channel, SCSI ID=7, 16/255 SCBs 
 (scsi0) Warning - detected auto-termination 
 (scsi0) Please verify driver detected settings are correct. 
 (scsi0) If not, then please properly set the device termination 
 (scsi0) in the Adaptec SCSI BIOS by hitting CTRL-A when prompted 
 (scsi0) during machine bootup. 
 (scsi0) Cables present (Int-50 NO, Int-68 NO, Ext-68 NO) 
 (scsi0) Downloading sequencer code... 413 instructions downloaded 
 (scsi1) <Adaptec AIC-7890/1 Ultra2 SCSI host adapter> found at PCI 10/0 
 (scsi1) Wide Channel, SCSI ID=7, 32/255 SCBs 
 (scsi1) Downloading sequencer code... 374 instructions downloaded 
 (scsi2) <Adaptec AIC-7880 Ultra SCSI host adapter> found at PCI 14/0 
 (scsi2) Wide Channel, SCSI ID=7, 16/255 SCBs 
 (scsi2) Downloading sequencer code... 413 instructions downloaded 

The aic7xxx driver has detected that my AHA-2940UW has termination
set to automatic. It doesn't like that. It is not clear to me why
the driver cares about the termination, but it clearly does. I 
set the termination manually using SCSI Select to LOW:on and 
HIGH on and the warning goes away:

 (scsi0) <Adaptec AHA-294X Ultra SCSI host adapter> found at PCI 14/0 
 (scsi0) Wide Channel, SCSI ID=7, 16/255 SCBs 
 (scsi0) Downloading sequencer code... 413 instructions downloaded 

Unfortunately, the SCSI bus works no better than before. I am 
out of ideas. I have a feeling that I am one switch away from the
thing working, but I have no idea where to look for the solution.

-Andy Smith (asmith at umdgrb.umd.edu)

A few more details:

the case is a Pacific Micro Data MAST 9500 configured with 8 disks 
on a single back plane and automatic termination. The disks are 
SEAGATE model ST150176LC 50Gb Ultra2 disks detected in the following 
manner (when connected to the AIC-7890 controller):

(scsi1:0:0:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sda at scsi1, channel 0, id 0, lun 0
(scsi1:0:1:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sdb at scsi1, channel 0, id 1, lun 0
(scsi1:0:2:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sdc at scsi1, channel 0, id 2, lun 0
(scsi1:0:3:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sdd at scsi1, channel 0, id 3, lun 0
(scsi1:0:8:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sde at scsi1, channel 0, id 8, lun 0
(scsi1:0:9:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sdf at scsi1, channel 0, id 9, lun 0
(scsi1:0:10:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02
Detected scsi disk sdg at scsi1, channel 0, id 10, lun 0
(scsi1:0:11:0) Synchronous at 40.0 Mbyte/sec, offset 15.
  Vendor: SEAGATE   Model: ST150176LC        Rev: 0002
  Type:   Direct-Access                      ANSI SCSI revision: 02

If it matters, the disks are configured as a raid-5 (7+1) software RAID
array, and are not used for system files.




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