Missing support for Iscsi multipath in nexentastore Cinder driver

[Avi Avraham]

While trying to configure Nexentastor community edition I failed to find any parameters repleted to Iscsi multipath configuration in the Cinder configuration file or in the openstack decontamination.

[Sean McGinnis (sean-mcginnis)]

It's possible they do not need any additional settings to support multipath. Hopefully someone from Nexenta can chime in here and possibly add to their documentation.

[Alexey Khodos (alexey-khodos)]

Hi, just as Sean said, we don't need any additional settings.
All you need is multipath tool installed on your client and enabled in nova.conf. Feel free to email me if you have any further question about using NexentaStor and cinder.

[Gorka Eguileor (gorka)]

I have looked into the Nexenta code and if it supports multipathing then it must be using discovery because looking at the driver code it relies on the cinder.volume.driver.ISCSIDriver code for the initialize connection, which uses the "provider_location" field from the volume that is filled by the "_do_export" method in cinder.volume.drivers.nexenta.iscsi.NexentaISCSIDriver.

And in that method we can see that it only adds 1 single portal:

            provider_location = '%(host)s:%(port)s,1 %(name)s %(lun)s' % {
                'host': self.nms_host,
                'port': self.configuration.nexenta_iscsi_target_portal_port,
                'name': target_name,
                'lun': entry['lun'],
            }

And since the ISCSIDriver code does not do discovery when the info is provided by the "provider_location" field the initialize_connection will return the data as if it were a single path.

So if will be in the os-brick code where we will be doing the iSCSI discovery and, if the backend is configured to do multipathing, hopefully we'll get a list of multiple portals we can use to do the multipathing.

[Alexey Khodos (alexey-khodos)]

Gorka, os-brick does the discovery before attaching the volume to instance. It uses the path returned by cinder in provider_location and discovers additional paths. It worked fine when I tested multipath with NexentaStor.

Is there a "best practice" on how to implement multipath? Should I use the initialize_connection method and returned multiple paths?