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Chapter VIII. iSCSI PDU Offload Initiator

1. Introduction

The Chelsio T4 series Adapters support iSCSI acceleration and iSCSI Direct Data Placement

(DDP) where the hardware handles the expensive byte touching operations, such as CRC

computation and verification, and direct DMA to the final host memory destination:

iSCSI PDU digest generation and verification

On transmitting, Chelsio h/w computes and inserts the Header and Data digest into the

PDUs. On receiving, Chelsio h/w computes and verifies the Header and Data digest of the

PDUs.

Direct Data Placement (DDP)

Chelsio h/w can directly place the iSCSI Data-In or Data-Out PDU's payload into pre-posted

final destination host-memory buffers based on the Initiator Task Tag (ITT) in Data-In or

Target Task Tag (TTT) in Data-Out PDUs.

PDU Transmit and Recovery

On transmitting, Chelsio h/w accepts the complete PDU (header + data) from the host

driver, computes and inserts the digests, decomposes the PDU into multiple TCP segments

if necessary, and transmit all the TCP segments onto the wire. It handles TCP

retransmission if needed.

On receiving, Chelsio h/w recovers the iSCSI PDU by reassembling TCP segments,

separating the header and data, calculating and verifying the digests, then forwarding the

header to the host. The payload data, if possible, will be directly placed into the pre-posted

host DDP buffer. Otherwise, the payload data will be sent to the host too.

The cxgb4i driver interfaces with open-iSCSI initiator and provides the iSCSI acceleration

through Chelsio hardware wherever applicable.

1.1. Hardware Requirements

1.1.1. Supported Adapters

The following are the currently shipping Chelsio Adapters that are compatible with iSCSI PDU

Offload Initiator Software:

T420-CR

T420-LL-CR

T440-CR

T440-LP-CR

T420-BCH

T422-CR

T420-CX

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Chelsio Communications Chelsio T4 Guía de usuario Pagina 131