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Date:      Sat, 5 May 2001 07:55:49 -0400
From:      Bill Pechter <pechter@ureach.com>
To:        "Ron Klinkien" <rklinkien@chello.nl>, freebsd-scsi@FreeBSD.ORG
Subject:   Re: Recovered data with positive head offset field replaceable unit msg
Message-ID:  <200105051155.HAA22713@stage21.ureach.com>

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> Hi SCSI wizards,
> 
> On one of my FreeBSD machines I found
> this rather strange scsi message:
> 
> > (da1:sym0:0:8:0): READ(06). CDB: 8 8 1 90 10 0
> > (da1:sym0:0:8:0): RECOVERED ERROR info:80198 asc:17,2
> (da1:sym0:0:8:0): Recovered data with positive head offset
field replaceable unit: df sks:80,12
> 
> Thanks in advance.
> 
> Regards,
> Ron.

Haven't seen something like that in years.
In the old days of SMD disks and DEC RP06's and RM05's (mid
80's), I'd have said it was a servo tracking issue with the
heads missing the data by a bit (possible bad spot on disk)
which was recovered by the disk controller offsetting the heads
a bit towards the center of the drive just a bit.

The data was recoverable... by the drive moving the head just a
little.  Things like this were caused by bad spot on disk (servo
platter or data platter) misalignment, dirt on the drive rails
that caused the heads to bounce a bit while seeking or trying to
stay on track, power fluctuations.  Some idiot banging into the
disks during a read operation.

Folks -- do things like this still happen with modern scsi
drives.  Misalignment is probably out.  Embedded servo's tend to
eliminate a weak servo head. Dirt on drive rails -- nah.

If it's a one shot error I wouldn't worry much -- but if it
reoccurs... it's a problem.

I've got a problem on one of the drives here that I know is the 

drive.da1: <SEAGATE SX910800N 8514> Fixed Direct Access SCSI-2
device
da1: 10.000MB/s transfers (10.000MHz, offset 15), Tagged
Queueing Enabled
da1: 8669MB (17755614 512 byte sectors: 255H 63S/T 1105C)

I get errors like this repeatedly on some parts of the disk:
I plan to reformat it... I've considered turning off tagged
queueing... 

sym0:1:control msgout: 80 20 79 d.
sym0:1:control msgout: 80 20 6b d.
(da1:sym0:0:1:0): WRITE(10). CDB: 2a 0 0 e2 4b 15 0 0 10 0
(da1:sym0:0:1:0): ABORTED COMMAND info:cf4b25 asc:4e,0
(da1:sym0:0:1:0): Overlapped commands attempted field
replaceable unit: 1

sym0:1:control msgout: 80 20 1b d.
sym0:1: message d sent on bad reselection.

--Bill


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