Справочник Пользователя для IBM Flex System V7000 Expansion Enclosure 4939H29

Draft Document for Review January 29, 2013 12:52 pm

IBM Flex System V7000 Storage Node Introduction and Implementation Guide

Multisession support, or host-level multipath support, provides multiple paths between iSCSI 
initiators and targets, which is 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. Once 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.

The following points apply to multisession configuration:

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The AIX iSCSI initiator does not support multisession.

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The use of the supported iSCSI multipathing is recommended when running the IO with 
multisession.

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If you use CHAP authentication under the Microsoft Windows operating system, use the 
same secret across each session that is initiated from that host to a particular target.

$$$$

$$

$

Best

Good

Adequate

No

Yes

Yes

None

iSCSI protocol 
management

iSCSI protocol 
management and TCP/IP 
protocol management

iSCSI read/write 
processing, TCP/IP 
processing, physical and 
data link communication

TCP/IP, physical and 
data link communication

Physical and data link 
communication

An HBA that provides 
Ethernet connectivity and 
additional functionality

A specialized NIC that 
provides additional 
functionality

Provides Ethernet
connectivity

$$$$

$$

$

Best

Good

Adequate

No

Yes

Yes

None

iSCSI protocol 
management

iSCSI protocol 
management and TCP/IP 
protocol management

iSCSI read/write 
processing, TCP/IP 
processing, physical and 
data link communication

TCP/IP, physical and 
data link communication

Physical and data link 
communication

An HBA that provides 
Ethernet connectivity and 
additional functionality

A specialized NIC that 
provides additional 
functionality

Provides Ethernet
connectivity