1.10. Configuring iSCSI Offload and Interface Binding
This chapter describes how to set up iSCSI interfaces in order to bind a session to a NIC port when using software iSCSI. It also describes how to set up interfaces for use with network devices that support offloading; namely, devices from Chelsio, Broadcom and ServerEngines.
The network subsystem can be configured to determine the path/NIC that iSCSI interfaces should use for binding. For example, if portals and NICs are set up on different subnets, then it is not necessary to manually configure iSCSI interfaces for binding.
Before attempting to configure an iSCSI interface for binding, run the following command first:
ping -I ethX target_IP[1]
If
ping fails, then you will not be able to bind a session to a NIC. If this is the case, check the network settings first.
1.10.1. Viewing Available iface Configurations
Red Hat Enterprise Linux 5.5 supports iSCSI offload and interface binding for the following iSCSI initiator implementations:
- Software iSCSI — like the
scsi_tcpandib_isermodules, this stack allocates an iSCSI host instance (i.e.scsi_host) per session, with a single connection per session. As a result,/sys/class_scsi_hostand/proc/scsiwill report ascsi_hostfor each connection/session you are logged into. - Offload iSCSI — like the Chelsio
cxgb3i, Broadcombnx2iand ServerEnginesbe2iscsimodules, this stack allocates ascsi_hostfor each PCI device. As such, each port on a host bus adapter will show up as a different PCI device, with a differentscsi_hostper HBA port.
To manage both types of initiator implementations,
iscsiadm uses the iface structure. With this structure, an iface configuration must be entered in /var/lib/iscsi/ifaces for each HBA port, software iSCSI, or network device (ethX) used to bind sessions.
To view available
iface configurations, run iscsiadm -m iface. This will display iface information in the following format:
iface_name transport_name,hardware_address,ip_address,net_ifacename,initiator_name
Refer to the following table for an explanation of each value/setting.
| Setting | Description |
|---|---|
iface_name | iface configuration name. |
transport_name | Name of driver |
hardware_address | MAC address |
ip_address | IP address to use for this port |
net_iface_name | Name used for the vlan or alias binding of a software iSCSI session. For iSCSI offloads, net_iface_name will be <empty> because this value is not persistent across reboots. |
initiator_name | This setting is used to override a default name for the initiator, which is defined in /etc/iscsi/initiatorname.iscsi |
The following is a sample output of the
iscsiadm -m iface command:
iface0 qla4xxx,00:c0:dd:08:63:e8,20.15.0.7,default,iqn.2005-06.com.redhat:madmax iface1 qla4xxx,00:c0:dd:08:63:ea,20.15.0.9,default,iqn.2005-06.com.redhat:madmax
For software iSCSI, each
iface configuration must have a unique name (with less than 65 characters). The iface_name for network devices that support offloading appears in the format transport_name.hardware_name.
For example, the sample output of
iscsiadm -m iface on a system using a Chelsio network card might appear as:
default tcp,<empty>,<empty>,<empty>,<empty> iser iser,<empty>,<empty>,<empty>,<empty> cxgb3i.00:07:43:05:97:07 cxgb3i,00:07:43:05:97:07,<empty>,<empty>,<empty>
It is also possible to display the settings of a specific
iface configuration in a more friendly way. To do so, use the option -I iface_name. This will display the settings in the following format:
iface.setting = value
Using the previous example, the
iface settings of the same Chelsio video card (i.e. iscsiadm -m iface -I cxgb3i.00:07:43:05:97:07) would appear as:
# BEGIN RECORD 2.0-871 iface.iscsi_ifacename = cxgb3i.00:07:43:05:97:07 iface.net_ifacename = <empty> iface.ipaddress = <empty> iface.hwaddress = 00:07:43:05:97:07 iface.transport_name = cxgb3i iface.initiatorname = <empty> # END RECORD
