Root/Documentation/scsi/cxgb3i.txt

1Chelsio S3 iSCSI Driver for Linux
2
3Introduction
4============
5
6The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc.
7series of products) support iSCSI acceleration and iSCSI Direct Data Placement
8(DDP) where the hardware handles the expensive byte touching operations, such
9as CRC computation and verification, and direct DMA to the final host memory
10destination:
11
12    - iSCSI PDU digest generation and verification
13
14      On transmitting, Chelsio S3 h/w computes and inserts the Header and
15      Data digest into the PDUs.
16      On receiving, Chelsio S3 h/w computes and verifies the Header and
17      Data digest of the PDUs.
18
19    - Direct Data Placement (DDP)
20
21      S3 h/w can directly place the iSCSI Data-In or Data-Out PDU's
22      payload into pre-posted final destination host-memory buffers based
23      on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT)
24      in Data-Out PDUs.
25
26    - PDU Transmit and Recovery
27
28      On transmitting, S3 h/w accepts the complete PDU (header + data)
29      from the host driver, computes and inserts the digests, decomposes
30      the PDU into multiple TCP segments if necessary, and transmit all
31      the TCP segments onto the wire. It handles TCP retransmission if
32      needed.
33
34      On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP
35      segments, separating the header and data, calculating and verifying
36      the digests, then forwarding the header to the host. The payload data,
37      if possible, will be directly placed into the pre-posted host DDP
38      buffer. Otherwise, the payload data will be sent to the host too.
39
40The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI
41acceleration through Chelsio hardware wherever applicable.
42
43Using the cxgb3i Driver
44=======================
45
46The following steps need to be taken to accelerates the open-iscsi initiator:
47
481. Load the cxgb3i driver: "modprobe cxgb3i"
49
50   The cxgb3i module registers a new transport class "cxgb3i" with open-iscsi.
51
52   * in the case of recompiling the kernel, the cxgb3i selection is located at
53    Device Drivers
54        SCSI device support --->
55            [*] SCSI low-level drivers --->
56                <M> Chelsio S3xx iSCSI support
57
582. Create an interface file located under /etc/iscsi/ifaces/ for the new
59   transport class "cxgb3i".
60
61   The content of the file should be in the following format:
62    iface.transport_name = cxgb3i
63    iface.net_ifacename = <ethX>
64    iface.ipaddress = <iscsi ip address>
65
66   * if iface.ipaddress is specified, <iscsi ip address> needs to be either the
67    same as the ethX's ip address or an address on the same subnet. Make
68    sure the ip address is unique in the network.
69
703. edit /etc/iscsi/iscsid.conf
71   The default setting for MaxRecvDataSegmentLength (131072) is too big;
72   replace with a value no bigger than 15360 (for example 8192):
73
74    node.conn[0].iscsi.MaxRecvDataSegmentLength = 8192
75
76   * The login would fail for a normal session if MaxRecvDataSegmentLength is
77    too big. A error message in the format of
78    "cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>."
79    would be logged to dmesg.
80
814. To direct open-iscsi traffic to go through cxgb3i's accelerated path,
82   "-I <iface file name>" option needs to be specified with most of the
83   iscsiadm command. <iface file name> is the transport interface file created
84   in step 2.
85

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