Re: iSCSI: Recovery R2T

[Parthi <pamanick@npd.hcltech.com>]

Hi Michael:

   Initiator will send SNACK request PDU indicates for missed numbered-response.

   Support for SNACK is mandatory only if the supported ErrorRecovery-
Level is greater than zero.

   The SNACK request is used to request the retransmission of numbered-
responses, data, or R2T PDUs from the target.

Draft says "

    The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
delivered as exact replicas of the ones the initiator missed and MUST
include all its flags. However, the fields ExpCmdSN, MaxCmdSN and Exp-
DataSN MUST carry the current values.

The numbered Data-In PDUs, requested by a SNACK with a RunLength dif-
ferent from 0, have to be delivered as exact replicas of the ones the
initiator missed and MUST include all its flags. However, the fields
ExpCmdSN and MaxCmdSN MUST carry the current values.  Data-In PDUs
requested with RunLength 0 (meaning all PDUs after this number) may be
different from the ones originally sent, in order to reflect changes
in MaxRecvPDULength.

Any SNACK that requests a numbered-response, Data, or R2T that was not
sent by the target MUST be rejected with a reason code of "Protocol
error". "
 

thanks,
parthi

"Mallikarjun C." wrote:

Michael,

It appears to me that we need to define the term `recovery R2T' -
the lack of which David Black also pointed out earlier.

Here's what I propose we should define it as:

Recovery R2T: It is an R2T generated by a target upon detecting
the loss of one or more Data-Out PDUs through one of the following means
- a digest error, a sequence error, or a sequence timeout.  A recovery
R2T carries the next unused R2TSN, but requests part of or the entire
data
burst that an earlier R2T (with a lower R2TSN) had already requested.

I believe the MUST/SHOULD/MAY language contained in Section 6 already
defines the expectations on the usage scope of recovery R2T.

 
--
Mallikarjun

Mallikarjun Chadalapaka
Networked Storage Architecture
Network Storage Solutions
MS 5668 Hewlett-Packard, Roseville.
cbm@rose.hp.com

> Michael Morrison wrote:
>
>
>
> If an initiator sends multiple Data-Out in response to an R2T, and one
> of the Data-Out in the
> sequence has a data digest error, can the recovery R2T solicit only
> the missing data, or must
> it solicit the whole sequence?   I can't find anything in the draft
> that defines what the contents
> of a recovery R2T MUST/SHOULD/MAY contain.
>
> Thanks
> Michael Morrison
> ISTOR Networks
> 7585 Irvine Center Dr. Ste 250
> Irvine Ca. 92618
> PGP Key: 74C30155

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