Wow there is a name I have not seen for awhile
dickens at us.ibm.com
Tue May 2 05:43:45 PDT 2006
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We what happens when you post to the reflector, you never know how will
harass you.. How have you been ? Are they keeping you busy ?
9000 South Rita Road
Tucson, Az, 85744
Tel: 520-799-4139 (T/L: 321-4139)
Email address: dickens at us.ibm.com
Gary.Franco at Emule
Sent by: To
owner-t10 at t10.org <David.Peterson at mcdata.com>,
<t10 at t10.org>, <t11_3 at t11.org>
05/01/2006 12:56 <Bob.Nixon at Emulex.Com>
RE: FCP-4: Items for discussion
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of David
Sent: Monday, May 01, 2006 2:23 PM
To: t10 at t10.org; t11_3 at t11.org
Subject: FCP-4: Items for discussion
Below is an email thread from Claudio that was discussed a bit at the last
FCP-4 working group meeting:
I please ask you to discuss in the FCP-4 WG the possibility to mandate
continuous increasing SEQ_CNT in FCP-4. Relying on it greatly simplifies
the detection of a missing Sequence and consequently simplifies error
recovery, but today is optional in FCP-x (while is mandated by IP over FC
and is going to be mandated by FC-SATA).
Additional items for FCP-4 discussion follows (all due to doubts submitted
- Bidirectional Commands: I think we need to count bytes for both data-in
and data-out. Which of these two counters should be put in the FC4VALUE
field of the REC ELS?
Wouldnât that be dependant on the type of command? FCP read or write types.
The device knows the current command type.
- Data Overlay: the FCP-3 definition of data overlay says "see SAM-3", but
SAM-3 says nothing on data overlay.
I would say that EMDP should be disabled cause with the end to end data
protection I do not think you can even enable this option because the DIFs
would get corrupted would they not?
- Data Overlay: In which way could it be possible detecting a missing
Sequence when data overlay is used and continuously increasing SEQ_CNT is
not used? (it seems to us that there is no way, but others may have a
I agree, I think there is no possible way, at least real-time as the data
is being streamed in. At FCP response time the overrun/underrun and
residual length would cause a re-execution of the command.
- Data Overlay: how can the FC4VALUE counters can be accurate when data
overlap (i.e., how to avoid to count twice the overlapping data)?
I would think that the ability to resend data blocks already sent was
discussed in the specification as a bad thing. If not then I believe the
only way to catch a misbehaving target would be to track the data blocks
already received and keep track of the holes left behind. The device would
also have to track the resent data and not include the resent data as data
received to satisfy a read command.
The members of the working group came to no real concensus/resolution per
the questions and would like to open up the discussion to the T10/T11
commitees, specifically making Continuously Increasing SEQ_CNT a
requirement for FCP-4.
Making this a requirement would be a much need improvement, and one that
has been needed for a while.
Regarding Continuously Increasing SEQ_CNT:
We have discussed requiring Continuously Increasing SEQ_CNT during each
previous FCP-x standard development efforts and folk opted to not specify
it as a requirement since some vendors did not yet fully support it. We may
have now moved past that issue.
Regarding Bidirectional Commands:
FCP-3 states: "Sequence level error recovery as described in 12.4 shall not
be used for bidirectional SCSI commands." So the question regarding the
FC4VALUE field is moot until if/when we want to support FCP-x error
detection and recovery for bidirectional commands.
Regarding Data Overlay:
The reference to SAM-3 is not intended to refer the reader to SAM-3 for
data overlay, but since it is outside the sentence this is what it means.
The reference will be removed since it provides value in this context
(i.e., the intent was to refer the reader to SAM-3 for application client
buffer offset but that is already covered).
The other two questions are vendor implementation specifc in my mind,
others may share if they wish...
More information about the T10