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IBM Flex System V7000 Storage Node Introduction and Implementation Guide
Figure 11-4 compares the features of iSCSI adapter options.
Figure 11-4 Comparison of iSCSI adapter technologies
11.3.3 iSCSI multisession configuration and support
Multisession support, or host-level multipath support, provides multiple paths between iSCSI
initiators and targets, which are used for high availability and load balancing.
Some products require that an iSCSI initiator log in with a specific IP address of the target
versus logging in with a target name. Logging in with a target name in those products causes
the iSCSI initiator to log into all of the IP addresses in the target and causes session
reinstantiation that results in session loss of the previous log in. Flex System V7000 Storage
Node offers single subnet multisession configurations and multiple and dual subnet
multisession configurations that remove the restriction against logging into a target name.
iSCSI initiators use Internet storage name service (iSNS) servers to log in, which enables the
discovery of the iSCSI targets and their IP addresses.
An iSCSI session is a TCP relationship between an iSCSI initiator node port and an iSCSI
target node port. After being established, iSCSI control, data, and status messages are
communicated over the session.
Each session is identified with multiple iSCSI initiator names and the target name plus the
iSCSI initiator session ID (ISID) plus the target portal group tag (target-side ID).
The Flex System V7000 Storage Node multisession approach is to have relationships
between multiple initiator instances (separate ISIDs) to a single target portal group in an
iSCSI target. Such an approach is similar to having multiple SCSI initiator ports from the
same iSCSI initiator device have relationships with a single SCSI target port.
$$$$ $$ $ Cost
Best Good Adequate iSCSI performance
No Yes Yes
Require software-
based initiator
None
iSCSI protocol
management
iSCSI protocol
management and TCP/IP
protocol management
Burden managed by
server CPU
iSCSI read/write
processing, TCP/IP
processing, physical and
data link communication
TCP/IP, physical and
data link communication Physical and data link
communication
Offloaded burden
An HBA that provides
Ethernet connectivity and
additional functionality A specialized NIC that
provides additional
functionality
Provides Ethernet
connectivity
Definition
iSCSI HBA TOE NIC
$$$$ $$ $ Cost
Best Good Adequate iSCSI performance
No Yes Yes
Require software-
based initiator
None
iSCSI protocol
management
iSCSI protocol
management and TCP/IP
protocol management
Burden managed by
server CPU
iSCSI read/write
processing, TCP/IP
processing, physical and
data link communication
TCP/IP, physical and
data link communication Physical and data link
communication
Offloaded burden
An HBA that provides
Ethernet connectivity and
additional functionality A specialized NIC that
provides additional
functionality
Provides Ethernet
connectivity
Definition
iSCSI HBA TOE NIC