multi-path IO in SCSI mid-layer

multi-path IO in SCSI mid-layer

[Patrick Mansfield]

Hi -

I'm interested in multi-path IO in the linux scsi mid-layer.

Are there developers working on changes to the scsi layers/interfaces?
I've seen references about such work, but no details.

Anyone else interested in or working on multi-path IO in the mid-layer?

I've looked at the code as to what changes might be required, and did
a simple prototype to issue IO requests using multiple paths for one device -
configuring one device in with multiple paths using SCSI INQUIRY page 0x83,
and selecting a path (just round-robin) at scsi_submit_cmd() time.

But, a decent multi-path IO implementation requires significant changes
to the current linux scsi interfaces/structures - especially where no
functional interfaces exist, such as the direct references to Scsi_Device
host, and Scsi_Host host_queue.

-- 
Patrick Mansfield
patman@sequent.com
patman@us.ibm.com

Re: multi-path IO in SCSI mid-layer

[Jason McMullan]

Patrick Mansfield <patman@sequent.com> wrote:
> I'm interested in multi-path IO in the linux scsi mid-layer.
>
> Are there developers working on changes to the scsi layers/interfaces?
> I've seen references about such work, but no details.
>
> [snip snip]
>
> But, a decent multi-path IO implementation requires significant changes
> to the current linux scsi interfaces/structures - especially where no
> functional interfaces exist, such as the direct references to Scsi_Device
> host, and Scsi_Host host_queue.

	At Linuxcare I have written a multi-path system for Linux 2.2.x
to support Sun's T3 hardware. It's pretty generic, though. (A user
in Europe has reported success with the IBM Shark SAN with our 
SCSI Alias Chains failover system).

	For source code, please see:

	http://open-projects.linuxcare.com/t3/

	Please contact me by email if you're interested in a version for 2.4.x.

-- 
Jason McMullan, Senior Linux Consultant
Linuxcare, Inc. 412.432.6457 tel, 412.656.3519 cell
jmcmullan@linuxcare.com, http://www.linuxcare.com/
Linuxcare. Putting open source to work.