[openib-general] [PATCH] IB/SRP: Enable multichannel

[Vu Pham]

Ishai Rabinovitz wrote:
> Hi Roland,
> 
> SRP High Availability needs an initiator to connect to the same target 
> several times, e.g., once from each IB port of the target (this way we can use
> device mapper multipath for failover). Note that both connections are actually
> active, e.g. multipath is issuing commands to to get the remote scsi id.
> 


It depends on how you define a path. An target-port-ID & 
initiator-port-ID tuple will form a path. Current srp 
implementation uses port GID as initiator_port_ID, and 
target ioc_guid + id_ext as target_port_ID. With this 
implementation, a physical host port & physical target port 
will form a path

multipath driver will see the same scsi_id of a lun thru 
multiple paths


> Since multiple channel operation is currently disabled in connection request,
> each new connection request will cause the target to disconnect
> the existing connection which forces us to bounce a lot between the two channels.

Either you can use multiple channels or derive different 
initiator_port_ID in the login req to have multiple paths on 
the same physical port

Most of srp targets that I tested don't support multiple 
channels.

-vu