85 lines
3.2 KiB
Plaintext
85 lines
3.2 KiB
Plaintext
Chelsio S3 iSCSI Driver for Linux
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Introduction
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============
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The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc.
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series of products) support iSCSI acceleration and iSCSI Direct Data Placement
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(DDP) where the hardware handles the expensive byte touching operations, such
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as CRC computation and verification, and direct DMA to the final host memory
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destination:
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- iSCSI PDU digest generation and verification
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On transmitting, Chelsio S3 h/w computes and inserts the Header and
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Data digest into the PDUs.
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On receiving, Chelsio S3 h/w computes and verifies the Header and
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Data digest of the PDUs.
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- Direct Data Placement (DDP)
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S3 h/w can directly place the iSCSI Data-In or Data-Out PDU's
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payload into pre-posted final destination host-memory buffers based
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on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT)
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in Data-Out PDUs.
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- PDU Transmit and Recovery
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On transmitting, S3 h/w accepts the complete PDU (header + data)
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from the host driver, computes and inserts the digests, decomposes
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the PDU into multiple TCP segments if necessary, and transmit all
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the TCP segments onto the wire. It handles TCP retransmission if
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needed.
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On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP
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segments, separating the header and data, calculating and verifying
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the digests, then forwarding the header to the host. The payload data,
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if possible, will be directly placed into the pre-posted host DDP
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buffer. Otherwise, the payload data will be sent to the host too.
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The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI
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acceleration through Chelsio hardware wherever applicable.
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Using the cxgb3i Driver
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=======================
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The following steps need to be taken to accelerates the open-iscsi initiator:
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1. Load the cxgb3i driver: "modprobe cxgb3i"
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The cxgb3i module registers a new transport class "cxgb3i" with open-iscsi.
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* in the case of recompiling the kernel, the cxgb3i selection is located at
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Device Drivers
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SCSI device support --->
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[*] SCSI low-level drivers --->
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<M> Chelsio S3xx iSCSI support
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2. Create an interface file located under /etc/iscsi/ifaces/ for the new
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transport class "cxgb3i".
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The content of the file should be in the following format:
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iface.transport_name = cxgb3i
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iface.net_ifacename = <ethX>
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iface.ipaddress = <iscsi ip address>
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* if iface.ipaddress is specified, <iscsi ip address> needs to be either the
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same as the ethX's ip address or an address on the same subnet. Make
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sure the ip address is unique in the network.
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3. edit /etc/iscsi/iscsid.conf
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The default setting for MaxRecvDataSegmentLength (131072) is too big;
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replace with a value no bigger than 15360 (for example 8192):
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node.conn[0].iscsi.MaxRecvDataSegmentLength = 8192
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* The login would fail for a normal session if MaxRecvDataSegmentLength is
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too big. A error message in the format of
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"cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>."
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would be logged to dmesg.
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4. To direct open-iscsi traffic to go through cxgb3i's accelerated path,
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"-I <iface file name>" option needs to be specified with most of the
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iscsiadm command. <iface file name> is the transport interface file created
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in step 2.
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