IBM Storwize V7000, Introduction And Implementation Manual

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Chapter 11. SAN connections and configuration
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Figure 11-3 compares the iSCSI initiator technologies.
Figure 11-3 Comparison of iSCSI initiator options
Software with hardware assistance
Hardware assistance in the context of an iSCSI software endpoint generally comes in the
form of a TCP offload engine (TOE). With a TOE, the TCP stack processing, including
framing, reordering of packets, check sums, and similar functions, are offloaded to a
dedicated card with its own network interface port. The TOE card can be a general-purpose
card that can offload TCP traffic, or it can be restricted to just accelerating iSCSI traffic.
TOE adapters benefit most from software initiators with additional host processor offload.
TOE adapters can also support advanced networking features such as link aggregation.
Because the software initiator is still used on the host, integration with layered management
applications is unaffected by the addition of the TOE hardware.
Hardware-only solutions
Hardware iSCSI adapters (hardware initiators) offload TCP stack processing functions and
iSCSI command processing functions. The hardware adapter looks and functions similar to a
SCSI disk interface, just as an FC HBA does. The operating system has no knowledge of the
underlying networking technology or interfaces. A separate management interface is used to
configure the networking parameters of the card.
Hardware-only solutions offload the largest amount of processing from the host processor.
Because they function as SCSI adapters, you can start an operating system from them if they
provide the appropriate host BIOS interfaces and are recognized as a startup device.
Advanced networking features might not be available because of software visibility to the
network functions in the card.
IBM Flex System V7000 Storage Node and some compute node adapters use iSCSI
hardware-only initiators. Other compute node adapters do have TOE capability.
Application
SCSI
Other
Protocols
iSCSI
TCP
IP
Network
Interface
Application
SCSI
Other
Protocols
iSCSI
TCP
IP
Network
Interface
Application
SCSI
iSCSI
TCP
IP
Network
Interface
NIC & iSCSI
Software
Initiator
TOE & iSCSI
Software
Initiator iSCSI HBA
Server
Processing
NIC/HBA
Processing