Re: iSCSI : Bridging missing CmdSNs and Abort I/O Error recovery

[Santosh Rao <santoshr@cup.hp.com>]

Julian,

2 issues are worth addressing in the I/O Error recovery descriptions :

1) How I/O error recovery is performed on a SCSI ULP timeout
detected by the initiator. Section 9 of the FC-PLDA document
is a good example of the type of error recovery description that
would be helpful.

I'm assuming that iSCSI expects initiators to use the Abort Task
or a higher level error recovery mechanism on a ULP timeout.
[unlike FC which defines a seperate ABTS-LS protocol for I/O
Error Recovery].

2) The technique[s] that should be used to bridge missing CmdSNs when an
initiator chooses not to "retry" a command on a connection failure or a digest

error, in order to prevent other CmdSNs ahead in the sequence from stalling,
awaiting receipt of the missing CmdSN.

Regards,
Santosh

julian_satran@il.ibm.com wrote:

> Santosh,
>
> You had a possible answer from Matt.  However I agree that we might want to
> address this in text although
> a solution similar to that suggested by Matt should be by now obvious to
> every implementer - the target should leave a placeholder in the input
> queue until the command after gets delivered.
>
> Julo
>
> Santosh Rao <santoshr@cup.hp.com> on 25/01/2001 21:38:04
>
> Please respond to Santosh Rao <santoshr@cup.hp.com>
>
> To:   IPS Reflector <ips@ece.cmu.edu>
> cc:
> Subject:  iSCSI : Bridging missing CmdSNs and Abort I/O Error recovery
>
> Julian & All,
>
> The draft is currently lacking a section that addresses abort I/O error
> recovery. Specifically, how is CmdSN bridging issues to be handled in
> the case where an initiator chooses not to retry an I/O [that failed on
> a connection failure that affects the delivery of the command to the
> target or a digest error at the target] because its ULP timer may have
> expired.
>
> In such cases, the initiator can send an Abort Task to inform the target
> that the I.T.T is being aborted and its corresponding CmdSN can be
> bridged, instead of having the target stall infinitely in its attempt to
> enforce ordering and await the missing CmdSN [which is'nt going to
> arrive, because the initiator did not retry the command].
>
> Regards,
> Santosh
>
>  - santoshr.vcf
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