Allow brick to support other iSCSI transports besides TCP¶

Problem description¶

open-iscsi has hardware iSCSI transport support. The interface argument specifies the hardware iSCSI interface to use for the operation. Any hardware vendors that currently provide hardware interfaces for open-iscsi cannot use them in openstack as the interfaces (iface) argument is not currently supported in the iSCSI driver.

Use Cases¶

Use of such iSCSI hardware transports requires providing a corresponding interface file (referred to as iface), which can be autogenerated via iscsiadm but need correctness checks or can also be generated on the fly, given the 3-tuple of ipaddress, hwaddress & transport name to be used. The iface format itself is generic and does not use any propreitary fields irrespective of transport being used.

These changes are already in nova, code can be seen here : https://review.openstack.org/#/c/146233/

This will also enable use of iSER directly through the iSCSI driver, though deprecating the iSER driver is not the aim of this spec, and will probably start with iSER disabled, (and also because iSER requires target support unlike hardware transports)

Proposed change¶

On the initiator side the only difference between using software iSCSI and hardware iSCSI transport is the interface flag (–interface=[iface])

e.g. “iscsiadm -m discovery -t st -p ip:port -I <iface file>”

iface files can automatically be generated for all hardware present on a system that is supported by open-iscsi by ‘iscsiadm -m iface’. The default format for iface file names is in the form <transport_name.hw_address>

The default iface name is ‘default’. Not using the -I parameter (which is how open-iscsi is currently being used in nova) is the same as specifying

‘iscsiadm -m discovery -t st -p ip:port -I default’

Required changes are :

• A new parameter to specify which transport should be used while doing iscsi discovery/login, falling back to TCP if operation does not succeed, or if parameter is not provided (-I default)
• Offloaded transports use the device path with a prefix pci-0000:00:00.0-, change related code to handle this

Implementation¶

Dependencies¶

None as such. However, the minimum information required for using a tansport if it is not already configured is a 3 tuple of ip, transport name & hardware address.

Testing¶

Current iSCSI tests will work just fine, run separately using a faux transport (open-iscsi already supports this ability)

Documentation Impact¶

Use of transport ifaces will need relevant documentation.

References¶

• https://bugs.launchpad.net/os-brick/+bug/1370226 (Launchpad bug this addresses)
• https://review.openstack.org/#/c/146233/ (Corresponding code in nova)
• http://www.open-iscsi.org/docs/README (Section 5.1 iSCSI iface setup)
• http://red.ht/1BJxsjL (Configuring an iface for iSCSI Offload, RedHat documentation)