SSC-4: Programmable Early Warning question

Kevin D Butt kdbutt at us.ibm.com
Fri Oct 2 10:12:02 PDT 2009


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r0910022_f.htm">HTML-formatted message</a>

Dennis,
The RECOVERED ERROR/PARAMETERS ROUNDED response is specified in SPC-4 for 
use when parameters are rounded.  This should be what we do at a minimum. 
There is no restriction on a volume being loaded and I suspect that the 
users of the PEWS would not want there to be this restriction.	This 
drives an implementer to either chose:
a)  a maximum supported value that is less than the native capacity of the 
volumes supported (though Set Capacity could mess that up); or
b) on volume state changing from unmounted to mounted, checking PEWS field 
and, if necessary, modify the value to the now current maximum value and 
establish a UA for MODE PARAMETERS CHANGED.
I am not sure that either solution is ideal, but I think either solution 
would work - or a combination of both where the UA would only be required 
if the capacity of a supported volume had been modified by a Set Capacity 
command to a capacity less than the value chosen for the maximum PEWS 
value supported.  I suspect that users would really only desire a max 
capacity of somewhere less than about 10 GB.  However, I don't think we 
should limit ourselves to that in the standard.
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/ 
From:
Dennis Painter <dennis at hale-pohaku.net>
To:
"t10 at t10.org" <t10 at t10.org>
Date:
10/02/2009 09:46 AM
Subject:
Re: SSC-4: Programmable Early Warning question
* From the T10 Reflector (t10 at t10.org), posted by:
* Dennis Painter <dennis at hale-pohaku.net>
*
Protection from it being set to a value greater that the media capacity 
is good. I favor recovered error as the software can accept it and 
continue or has the option to read the PEWS setting.
Is it allowed for the application client to set PEWS if there is no 
media present? I did not find a restriction in the current draft but it 
may not be where I looked.
If not restricted and media of different capacity is supported then 
there is a potential problem of PEWS being set for a larger capacity 
tape and having a smaller capacity tape inserted. If PEWS is cleared on 
media removal and cannot be set without media present then there would 
be no issue.
Dennis Painter
Ballard, Curtis C (StorageWorks) wrote:
> In the interest of having a complete specification it would be 
> appropriate to specify behavior although I would hope that an 
> application would never make that mistake.
> 
> Rather than reject the command I would be inclined to have a device 
> specific maximum PEWS zone and report a recovered error with the PEWS 
> zone set to the maximum allowed.
> 
> Curtis Ballard
> Hewlett Packard
>
> ------------------------------------------------------------------------
> *From:* owner-t10 at t10.org [mailto:owner-t10 at t10.org] *On Behalf Of 
> *Kevin D Butt
> *Sent:* Thursday, October 01, 2009 1:46 PM
> *To:* t10 at t10.org
> *Subject:* SSC-4: Programmable Early Warning question
>
>
> Tapeheads,
>
> I wonder if we should protect the programmable early warning from 
> being set to too large a value.  Should we add some statement like the 
> following to SSC-4?
>
> If PEWS field of Device Configuration Extension mode page is set to a 
> value larger than the tapes capacity, then the Mode Select should be 
> rejected with ILLEGAL REQUEST, INVALID FIELD IN PARAMETER LIST.
>
> Thanks,
>
> Kevin D. Butt
> SCSI & Fibre Channel Architect, Tape Firmware
> MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
> Tel: 520-799-5280
> Fax: 520-799-2723 (T/L:321)
> Email address: kdbutt at us.ibm.com
> http://www-03.ibm.com/servers/storage/ 
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Protection from it being set to a value greater that the media capacity is 
good. I favor recovered error as the software can accept it and continue 
or has the option to read the PEWS setting.
Is it allowed for the application client to set PEWS if there is no media 
present? I did not find a restriction in the current draft but it may not 
be where I looked.
If not restricted and media of different capacity is supported then there 
is a potential problem of PEWS being set for a larger capacity tape and 
having a smaller capacity tape inserted. If PEWS is cleared on media 
removal and cannot be set without media present then there would be no 
issue.
Dennis Painter
Ballard, Curtis C (StorageWorks) wrote: 
>In the interest of having a complete specification it would be 
appropriate to specify behavior although I would hope that an application 
would never make that mistake.
> 
>Rather than reject the command I would be inclined to have a device 
specific maximum PEWS zone and report a recovered error with the PEWS zone 
set to the maximum allowed.
> 
>Curtis Ballard
>Hewlett Packard
>
>
>----------
>From: <mailto:owner-t10 at t10.org>owner-t10 at t10.org [
mailto:owner-t10 at t10.org] On Behalf Of Kevin D Butt
>Sent: Thursday, October 01, 2009 1:46 PM
>To: <mailto:t10 at t10.org>t10 at t10.org
>Subject: SSC-4: Programmable Early Warning question
>
>
>Tapeheads, 
>
>I wonder if we should protect the programmable early warning from being 
set to too large a value.  Should we add some statement like the following 
to SSC-4? 
>
>If PEWS field of Device Configuration Extension mode page is set to a 
value larger than the tapes capacity, then the Mode Select should be 
rejected with ILLEGAL REQUEST, INVALID FIELD IN PARAMETER LIST. 
>
>Thanks, 
>
>Kevin D. Butt
>SCSI & Fibre Channel Architect, Tape Firmware
>MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
>Tel: 520-799-5280
>Fax: 520-799-2723 (T/L:321)
>Email address: kdbutt at us.ibm.com
>http://www-03.ibm.com/servers/storage/ 
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