Chelsio Communications Terminator 6, Инструкция по установке и эксплуатации, Страница: 188 / 432

Chapter XI. iSCSI PDU Offload Initiator
Chelsio Unified Wire for Linux 188
Introduction
The Chelsio Unified Wire series of 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 transmit -side, Chelsio hardware computes and inserts the Header and Data digest into
the PDUs. On receive-side, Chelsio hardware computes and verifies the Header and Data
digest of the PDUs.
•
Direct Data Placement (DDP)
Chelsio hardware can directly place the iSCSI Data-In or Data-Out PDU's payload into pre-
posted 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 transmit-side, Chelsio hardware accepts the complete PDU ( 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 receive-side, Chelsio hardware 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 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
Supported adapters
The following are the currently shipping Chelsio adapters that are compatible with iSCSI PDU
Offload Initiator Software:
T62100-CR
T62100-LP-CR
T6425-CR
T6225-CR
T6225-LL-CR
T6225-SO-CR^
T580-CR