Background operations and power loss expected

[Ralph Weber]

* From the T10 Reflector (t10 at t10.org), posted by:
* Ralph Weber <roweber at ieee.org>
*
For what is is worth, the people working on third-party copy
have concluded that the correct thing to do with a background
copy operation (e.g., a copy operation started by a command
with the Immed bit set to one) is to abort the background
copy operation if an I_T nexus loss occurs.
With this in mind, I anticipate that a new third-party copy
proposal revision will ask that the troublesome sentence be
modified to read:
"Unless otherwise specified, background operations shall not
be aborted by I_T nexus loss or power loss expected."
All the best,
.Ralph
On 10/7/2011 12:58 PM, Gerry Houlder wrote:
> The only problem with that is our rules for resolving conflicts 
> between standards says SAM-5 prevails over SPC-4. Unless we change 
> SAM-5, the SAM-5 words override. I agree with you that CAP decided 
> what should happen.
>
> On Fri, Oct 7, 2011 at 12:06 PM, Mark Evans <Mark.Evans at wdc.com 
> > wrote:
>
>     Hi Gerry,
>
>     Proposal 10-144 was intended to clarify the definition of the
>     self-test functions and was discussed at length during two CAP
>     working group meetings.  Power loss expected is a relatively new
>     feature developed long after self-test, and definition of the
>     behavior regarding that event relative to self-test was included
>     in the proposal to help with the clarification.  I remember that
>     we specifically discussed what the behavior for a power loss
>     expected event should be during development of the proposal in a
>     CAP, which resulted in the sentence, “A SCSI target device shall
>     abort a self-test being performed in the background mode as the
>     result of a power loss expected event…”  This sentence is clear
>     and specific, and I think it overrides any other ambiguity.
>      However, as always, I would welcome a detailed proposal from
>     someone to clarify or correct what they see as ambiguities or
>     errors in a T10 standard in the manner I did with 10-144.
>
>     Please feel free to call or send an email to me with any comments
>     or questions that you have about this stuff.
>
>     Regards,
>
>     Mark Evans
>     Western Digital Corporation
>     5863 Rue Ferrari
>     San Jose, CA 95138
>     Email: mark.evans at wdc.com 
>
>     *From:*owner-t10 at t10.org <mailto:owner-t10 at t10.org>
>     [mailto:owner-t10 at t10.org <mailto:owner-t10 at t10.org>] *On Behalf
>     Of *Gerry Houlder
>     *Sent:* Friday, October 07, 2011 6:31 AM
>
>
>     *To:* T10 Reflector
>     *Subject:* Re: Background operations and power loss expected
>
>     It seems like there are some contradictions among SAM-5 and SPC-4.
>     This should become an agenda item for the November CAP meeting.
>
>     On Fri, Oct 7, 2011 at 3:09 AM, Truong Nguyen - SISA
>     <tru.nguyen at sisa.samsung.com >
>     wrote:
>
>     Here is the representative text from SAM5r07 sub-clause 5.5:
>
>     "Some commands initiate background operations that are processed
>     after the command is no longer in the task set (i.e., status has
>     been returned for the command) (e.g., a SEND DIAGNOSTIC command
>     when used to initiate a background self-test (see SPC-4) or a
>     write command when write cache is enabled (see SBC-3)). Background
>     operations may be aborted by power on, hard reset, or logical unit
>     reset. Background operations shall not be aborted by I_T nexus
>     loss or power loss expected."
>
>     The Send Diagnostic initiated background self test is described as
>     an example of a "background operation" as defined by SAM-5. This
>     is distinct from the "device specific background function" as
>     defined in SPC4r32, which explicitly excludes the Send Diagnostic
>     initiated background self test.
>
>     SAM5r07 defines "background operations" as follows:
>
>     "*3.1.9 background operation: *An operation started by a command
>     that continues processing after the command is no longer in the
>     task set."
>
>     This definition would seem to define a background operation as
>     those initiated by the application client.
>
>     Here is the relevant text from SPC4r32, with the power loss
>     expected event handling introduced by 10-144r3:
>
>     "An application client may request that a device server abort a
>     self-test that is being performed in the background mode by
>     sending a SEND DIAGNOSTIC command with the SELF-TEST CODE field
>     set to 100b (i.e., abort background self-test function). A SCSI
>     target device shall not abort a self-test being performed in the
>     background mode as the result of an I_T nexus loss event (see
>     SAM-4). A SCSI target device shall abort a self-test being
>     performed in the background mode as the result of a power loss
>     expected event (see SAM-4)."
>
>     10-144r3 introduced the notion that a power loss expected event
>     shall not abort the background self-test, which appears to
>     conflict with SAM5r07 (and SAM4).
>
>     Truong
>
>    
------------------------------------------------------------------------
>
>     *From:*owner-t10 at t10.org <mailto:owner-t10 at t10.org>
>     [mailto:owner-t10 at t10.org] <mailto:[mailto:owner-t10 at t10.org]> *On
>     Behalf Of *Gerry Houlder
>     *Sent:* Wednesday, October 05, 2011 11:15 AM
>     *To:* T10 Reflector
>     *Subject:* Re: Background operations and power loss expected
>
>     We tend to think of the device self-test that is kicked off via a
>     SEND DIAGNOSTIC command to be a host initiated background task,
>     whereas most other background tasks (e.g., background medium scan)
>     are device initiated. I think this accounts for the conflict.
>
>     Perhaps SAM-5 should change wording to "Target device initiated
>     background operations shall not be aborted ...". I think the SEND
>     DIAGNOSTIC command case is the only host initiated background
>     operation that is defined in SCSI.
>
>     On Wed, Oct 5, 2011 at 12:14 PM, Truong Nguyen - SISA
>     <tru.nguyen at sisa.samsung.com >
>     wrote:
>
>     In 10-144r3 (SPC:4 Self-test and SEND DIAGNOSTIC command
>     clean-up), text was added to the Self-test operations Background
>     mode model clause, specifying changes regarding power loss
>     expected handling. Specifically, in sub-clause 5.8.4.3 Background
>     mode (SPC-4r32), the following text was added:
>
>     "A SCSI target device shall abort a self-test being performed in
>     the background mode as the result of a power loss expected event
>     (see SAM-4)."
>
>     However, in SAM-4r14 (and in SAM-5r07), the following text is
>     present in sub-clause 5.5 Command lifetime:
>
>     "Background operations shall not be aborted by I_T nexus loss or
>     power loss expected."
>
>     When a power loss expected event occurs, which is the correct
>     behaviour in terms of the background self-test? Should it be
>     aborted or not be aborted?
>
>     Thanks,
>
>     Truong Nguyen
>
>     Samsung Information Systems
>
>
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