RE: iSCSI Target Reset

[Black_David@emc.com]

Starting with John's comments:

> described the action in FC terms.  In iSCSI terms, I think the Target
> Device would be a complete Symmetrix.  Do you think that is correct?

If existing cluster software continues to issue Target Resets, then
no, because such Target Resets must not reset the complete
Symmetrix for correct operation - they don't currently.

> What does Symmetrix do today to support Target Reset?

Reset the port on which it arrives (SCSI or FC), and generally
configure things so that anything else that could be negatively
impacted by side effects of that reset is not connected to that port.
IIRC, AIX clusters use Target Resets.

> And how do you think it should act in the future?

Whatever it takes to keep existing cluster software happy.

> Surly you do not want the complete controller reset, do you?

If "controller" means the entire array, then of course not -
don't be ridiculous.

On to Rob's most important comment:

> The recent SAM-2 change was expressly designed to encourage 
> iSCSI and SRP to drop support for TARGET RESET.  Please don't 
> keep it because you think T10 would be offended :-)

If dropping support for it breaks existing clustering software, that doesn't
seem like a good idea.  Such breakage will be viewed as an iSCSI
problem (it works fine on Fibre Channel ...), and will not contribute
to the adoption or acceptance of iSCSI :-(.

I appreciate T10's intention to obsolete Target Reset and would offer
two possible courses of action:

- If someone writes up a convincing case (Internet-Draft) for being
	able to map things that would have caused Target Resets to
	LUN Resets in iSCSI device drivers and the like in a fashion that
	will keep existing cluster software working (and unaware that
	this change has happened beneath it), then dropping
	Target Reset may be feasible.  This is akin to the discussion
	we went through about mandating Autosense and dropping
	Contingent Allegiance (it's easy to make a CA device do
	Autosense transparently), except that it'll have to consider what
	the various clustering software implementations actually do,
	as opposed to all the possible ways in which Target Reset
	could be used/abused.  Anyone want to volunteer?

- Put in some SHOULDs and SHOULD NOTs encouraging the use
	of LU Reset in place of Target Reset, and making Target Reset
	either OPTIONAL or NOT RECOMMENDED to implement.

The second bullet seems to match what T10 has done in practice
- this feature is not a good idea, but can't be removed from the
specification, at least not yet.

One more question for T10 - do the tape folks still need Target
Reset to whack an uncooperative robot/drive into submission
or is LU Reset good enough?

Comments?

Thanks,
--David

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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
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