FCP-2 recovery problem

Baldwin, Dave Dave.Baldwin at emulex.com
Tue Jun 20 18:42:06 PDT 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* "Baldwin, Dave" <Dave.Baldwin at emulex.com>
*
This is a multi-part message in MIME format.
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After considering several solutions to this issue, I have come up with
the attached proposal to solve the problem. Since Emulex is not a T10
member, I am not sure where to put the proposal, or how to number it.
Any guidance in this area would be appreciated.

There are other potential solutions to the problem, but they are
generally more complex and cause performance degradation. Matt's
suggestion to use FCP_CONF and then send REC to make sure the FCP_CONF
made it to the target would have to be used on all non-write commands,
thus degrading performance (but it does work).

There are OX_ID games one could play, but they would require lengthy
delays in releasing resources, or complex queuing behaviors that will
cause problems or performance degradation  in some  implementations.
Here is an example of a hole one could hit trying to control OX_ID use:

Behavior: Control the OX_ID such that there are never two identical
consecutive OX_IDs sent to an FCP-2 LUN.

Flaw: This behavior would fail in a multi-LUN FCP-2 target. Here is one
scenario:

Command1 -----> OX_ID=1, LUN=0
OX_ID=1     <----- Response1

(Send 64k other commands to other targets in less than 2 seconds)

Command2 ------> OX_ID=1, LUN=1   X (command dropped)

REC             -------> OX_ID=1, RX_ID=0xFFFF

Good response sent <------- ACC

The Initiator sent the REC to check on Command2 to LUN=1. The target
sent an ACC with information about Command1 to LUN=0. This leads to
invalid recovery. Controlling OX_ID reuse to a LUN is not sufficient to
solve this problem.

Please review the attached proposal and send your comments back to the
reflector.

Best regards,
Dave Baldwin
Emulex Corporation


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