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25.14. 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.
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
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.
25.14.1. Viewing Available iface Configurations
iSCSI offload and interface binding is supported for the following iSCSI initiator implementations:
- Software iSCSI
- This stack allocates an iSCSI host instance (that is,
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
- This stack allocates a
scsi_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 |
Example 25.6. Sample Output of the iscsiadm -m iface Command
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.
Example 25.7. iscsiadm -m iface Output with a Chelsio Network Card
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
Example 25.8. Using iface Settings with a Chelsio Converged Network Adapter
Using the previous example, the
iface settings of the same Chelsio converged network adapter (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
25.14.2. Configuring an iface for Software iSCSI
As mentioned earlier, an
iface configuration is required for each network object that will be used to bind a session.
Before
To create an
iface configuration for software iSCSI, run the following command:
# iscsiadm -m iface -I iface_name --op=new
This will create a new empty
iface configuration with a specified iface_name. If an existing iface configuration already has the same iface_name, then it will be overwritten with a new, empty one.
To configure a specific setting of an
iface configuration, use the following command:
# iscsiadm -m iface -I iface_name --op=update -n iface.setting -v hw_address
Example 25.9. Set MAC Address of iface0
For example, to set the MAC address (
hardware_address) of iface0 to 00:0F:1F:92:6B:BF, run:
# iscsiadm -m iface -I iface0 --op=update -n iface.hwaddress -v 00:0F:1F:92:6B:BF
Warning
Do not use
default or iser as iface names. Both strings are special values used by iscsiadm for backward compatibility. Any manually-created iface configurations named default or iser will disable backwards compatibility.
25.14.3. Configuring an iface for iSCSI Offload
By default,
iscsiadm creates an iface configuration for each port. To view available iface configurations, use the same command for doing so in software iSCSI: iscsiadm -m iface.
Before using the
iface of a network card for iSCSI offload, first set the iface.ipaddress value of the offload interface to the initiator IP address that the interface should use:
- For devices that use the
be2iscsidriver, the IP address is configured in the BIOS setup screen. - For all other devices, to configure the IP address of the
iface, use:# iscsiadm -m iface -I iface_name -o update -n iface.ipaddress -v initiator_ip_address
Example 25.10. Set the iface IP Address of a Chelsio Card
For example, to set the
iface IP address to 20.15.0.66 when using a card with the iface name of cxgb3i.00:07:43:05:97:07, use:
# iscsiadm -m iface -I cxgb3i.00:07:43:05:97:07 -o update -n iface.ipaddress -v 20.15.0.66
25.14.4. Binding/Unbinding an iface to a Portal
Whenever
iscsiadm is used to scan for interconnects, it will first check the iface.transport settings of each iface configuration in /var/lib/iscsi/ifaces. The iscsiadm utility will then bind discovered portals to any iface whose iface.transport is tcp.
This behavior was implemented for compatibility reasons. To override this, use the
-I iface_name to specify which portal to bind to an iface, as in:
# iscsiadm -m discovery -t st -p target_IP:port -I iface_name -P 1 [5]
By default, the
iscsiadm utility will not automatically bind any portals to iface configurations that use offloading. This is because such iface configurations will not have iface.transport set to tcp. As such, the iface configurations need to be manually bound to discovered portals.
It is also possible to prevent a portal from binding to any existing
iface. To do so, use default as the iface_name, as in:
# iscsiadm -m discovery -t st -p IP:port -I default -P 1
To remove the binding between a target and
iface, use:
# iscsiadm -m node -targetname proper_target_name -I iface0 --op=delete[6]
To delete all bindings for a specific
iface, use:
# iscsiadm -m node -I iface_name --op=delete
To delete bindings for a specific portal (e.g. for Equalogic targets), use:
# iscsiadm -m node -p IP:port -I iface_name --op=delete
Note
If there are no
iface configurations defined in /var/lib/iscsi/iface and the -I option is not used, iscsiadm will allow the network subsystem to decide which device a specific portal should use.
