Presentation on theme: "SCSI Command ordering & iSCSI Rob Elliott Mallikarjun Chadalapaka."— Presentation transcript:
SCSI Command ordering & iSCSI Rob Elliott Mallikarjun Chadalapaka
page 218 March 2003 Rob Elliott, Mallikarjun Chadalapaka, HP Intent There have been several iterations of IPS list discussion during the last couple of years on the entire notion of command ordering in iSCSI. – There are multiple related SCSI concepts and there is no “glue” document that says what is (appropriately) unsaid both in the T10 specs and the iSCSI spec. – It also became clear that a document that explains the iSCSI design rationale behind ordering concepts could help iSCSI implementers internalize the iSCSI concepts much better, leading to hopefully better iSCSI interoperability. The draft-chadalapaka-command-ordering-00 draft is thus produced with the following goals: – explain design considerations that led to the iSCSI session model as it is defined today – relate the SCSI command ordering features defined in T10 specifications to the iSCSI concepts – provide guidance to system designers on how true command ordering solutions can be designed and built deploying iSCSI. This draft is currently proposed to be an informational draft.
page 318 March 2003 Rob Elliott, Mallikarjun Chadalapaka, HP Draft Overview Makes the design intent of the iSCSI spec clear wrt command ordering – The service delivery subsystem abstraction provided by an iSCSI session has the intrisic property of ordered command delivery. – Target iSCSI must always ensure that ordered commands are delivered to local SCSI layer, while initiator generally has the discretion of when to utilize this ordered delivery. Relates the SCSI ordering features to iSCSI’s command ordering – SCSI defines ACA, CRN, ORDERED and other task attributes, and UA- interlock. – Certain iSCSI protocol requirements (task termination status on connection failure) are intended to allow usage of ACA or UA-interlock by the initiator. Provides guidance to implementers on related system design issues – iSCSI target designers, especially those of streaming devices, must of course support command queueing in order for command ordering to be valuable. – iSCSI target designers should consider supporting ORDERED/SIMPLE task attributes to enable command ordering solutions.
page 418 March 2003 Rob Elliott, Mallikarjun Chadalapaka, HP Summary Questions Are there review comments? Other feedback? Any relevant technical information currently missing? The authors of draft-chadalapaka-command-ordering-00.txt makes a motion that the IPS WG adopt this document as an official workgroup item to enable eventual publication as an informational RFC.