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Chapter 24
Configuring IP Storage
Setting the QOS Values
To set the QoS values, follow these steps:
Choose Interfaces > FC Logical from the Fabric Manager Physical Attributes pane, or choose
Step 1
Interfaces > Ethernet or iSCSI from Device Manager. You see the Interface tables in the Fabric
Manager Information pane, or the Device Manager Interfaces dialog box.
Click the iSCSI TCP tab. You see the iSCSI TCP configuration table.
Step 2
Set the QoS field from 1 to 6.
Step 3
Click the Apply Changes icon in Fabric Manager (or click Apply in Device Manager) to save these
Step 4
changes, or click Undo Changes in Fabric Manager (or click Cancel in Device Manager) to discard
changes.
iSCSI Forwarding Mode
The iSCSI gateway on the IPS module has two modes of forwarding operation
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iSCSI High Availability
The following high availability features are available for iSCSI configurations:
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Multiple IPS Ports Connected to the Same IP Network
Figure 24-29
same IP network.
OL-7753-01
The pass-thru mode (default)—In this mode, the IPS port converts an iSCSI PDU into an FCP frame
or vice versa and then forwards it one frame or PDU at a time. The absence of buffering PDUs or
frames keeps the operation latency low. To operate in this mode, the IPS port has to negotiate with
its peers a suitable maximum size of the data payload in each frame/PDU. This is done during iSCSI
login and FC PLOGI and the value is restricted by the TCP connection's Maximum Segment Size
(MSS) and the maximum Fibre Channel data payload size specified by the FC target. This usually
results in a smaller maximum payload size than most hosts expect, thus comes the second mode of
forwarding.
The store-and-forward mode—This mode allows the iSCSI client to send and receive an iSCSI data
payload at the size it desires. This sometimes results in better performance for the client. The IPS
port stores each TCP segment it receives until one full iSCSI PDU is received before converting and
forwarding it as Fibre Channel frames to the FC target. In the opposite direction, the IPS port
assembles all FC data frames of an exchange to build one iSCSI data-in PDU before forwarding it
to the iSCSI client. The limitation on this mode is iSCSI CRC data digest cannot be used.
Multiple IPS Ports Connected to the Same IP Network
VRRP-Based High Availability
Ethernet PortChannel-Based High Availability
provides an example of a configuration with multiple Gigabit Ethernet interfaces in the
Cisco MDS 9000 Fabric Manager Switch Configuration Guide
Configuring iSCSI
24-39
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