multipath selection based on queue length

[Fraser Campbell <fraser@georgetown.wehave.net>]

Hi,

Our SAN group would like us to balance I/O requests across all paths 
based on queue length.  My understanding of this is that we would 
essentially route each I/O request down the path with fewest pending I/O 
requests (perhaps my understanding is overly simplistic).

Is this possible with dm-multipath, multipath-tools, etc?  I am running 
SLES 9 which includes dm-multipath 1.0.4 and multipath-tools 0.4.5.

The SAN is a Hitachi Tagma, here is one test LUN:

   350060e80000000000000a95200000480
   [size=13 GB][features="0"][hwhandler="0"]
   \_ round-robin 0 [enabled][best]
     \_ 0:0:0:36 sde  8:64    [active]
   \_ round-robin 0 [enabled]
     \_ 1:0:0:36 sdj  8:144   [active]

That is default config, I have also setup with multibus but our SAN 
group does not want us to use round-robin load balancing, nor do they 
want us to use single-path I/O as we would get with the failover approach.

Any suggestions?

Thanks,
Fraser