Elimination of EFW

Bob Snively Bob.Snively at Eng.Sun.COM
Fri Mar 15 21:45:47 PST 1996

* From the SCSI Reflector, posted by:
* Bob.Snively at Eng.Sun.COM (Bob Snively)


The EFW (Enclosure Failure Warning) should be removed from the
definition of the drive-to-enclosure interface in the SFF-8045 and
SFF-8046 documents and the relevant MODE SENSE/SELECT page functions 
removed from the proposed SCSI Enclosure Services document.


As part of the SAF-TE and SCSI-3 Environmental Services activity, the
EFW function was carefully considered.  After that effort, it was decided
to that the function should be removed for the following reasons.

a)	No one in the consulted organizations has any intent of
	using the function.

b)	All disk drives already protect data during loss of power.
	Writing is stopped by hardware as soon as power drops below
	a certain required value.  At that time, no more data is
	written.  No data outside the block being written is damaged.

c)	The time delay between the time that the enclosure detects 
	a warning condition and the time the disk drive looses the
	necessary capabilities to perform protective actions is
	extremely variable.  It is probably not long enough in
	most cases to perform any of the protective actions except
	those that are already provided by the normal loss of
	power protection.

d)	Disk drive manufacturers have indicated that the
	function requires significant hardware support not already
	available in their designs.  The redesign of a disk
	drive to support an unused function of questionable value
	has been resisted by all disk drive manufacturers.

e)	One company has been found to have historically used the
	function, but their representatives indicate that present
	implementations do not use the function and they feel no 
	need for the function.


Enclosure Failure Warning (EFW) was proposed originally as an
indication made available from an enclosure to a disk drive to
warn the disk drive that it would be loosing the support of
the enclosure (particularly power) very shortly.  An optional 
action, selected by the proper setting of a MODE SENSE/SELECT
page, would be performed when the warning was detected.

The alternative actions that could be selected included:

	a)	A vendor unique action 

	b)	Termination of the write at a block boundary,
		followed by a reset of all internal activities.

	c)	A termination of the write at a command boundary
		and the temporary suspension of on-going activities.

	d)	All commands continue, but an informational
		exception is posted to indicate an EFW occurred.

Last documented by X3T10/95-324, revision 2.1.  Removed in revision 3.0.

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