Proposal to add a new modifier to SCSI Write commands. (fwd)

[John Lohmeyer - SCSI]

* From the SCSI Reflector (scsi at symbios.com), posted by:
* John Lohmeyer - SCSI <jlohmeye>
*
Another message send to the reflector administrative address instead
of to scsi at symbios.com ...

Milton Scritsmier wrote:
From: Milton Scritsmier <milton at arraytech.com>
Subject: Re: Proposal to add a new modifier to SCSI Write commands.
To: owner-scsi at Symbios.COM
Date: Mon, 2 Dec 1996 13:36:43 -0700 (MST)
In-Reply-To: <96120214084546 at star.zko.dec.com> from "Tom" at Dec 2, 96 02:08:46 pm
Reply-To: milton at arraytech.com (Milton Scritsmier)

Tom wrote:
> 
> 
> * From the SCSI Reflector (scsi at symbios.com), posted by:
> * coughlan at star.zko.dec.com (Tom)
> *
> >> The host gets an unrecovered read error,
> >> so it will not reassign the block.  
> 
> No, this is written the way I meant it, though I agree this host behavior
> is not in the Standard, and is not required.  
> 
> Generally, when a host gets an unrecovered read error it has no way to know
> what data was supposed to be in the block.  Host-initiated Reassignment is
> a bad thing to do in this case, because subsequent reads of the block will
> succeed, but the data they deliver will be garbage as far as the
> application is concerned.  The host should only Reassign when it knows what
> to put in the new block (that is, after a failed Write or a Recovered Read).
> 
> Maybe your system works differently?

You exclude the case where the host can get the correct data from someplace
else. This would include such things as a mirror disk or from the other
disks in a RAID 5 redundancy group containing the disk with the read error.
While this may not be the case for many host systems, we do this in our
RAID disk array and I expect other disk array vendors do the same thing as
well.

   Milton Scritsmier
   Array Technology, a division of EMC Corp.
   Boulder, CO

   milton at arraytech.com




-- 
John Lohmeyer               E-Mail: john.lohmeyer at symbios.com
Symbios Logic Inc.           Voice: 719-533-7560 Fax: 719-533-7036
4420 ArrowsWest Dr.            WWW: www.symbios.com/x3t10
Colo Spgs, CO 80907-3444  SCSI BBS: 719-533-7950 300--14400 baud
*
* For SCSI Reflector information, send a message with
* 'info scsi' (no quotes) in the message body to majordomo at symbios.com