RFC: GEOM MULTIPATH rewrite

[Nikolay Denev]

On 20.01.2012, at 12:51, Alexander Motin <mav at freebsd.org> wrote:

> On 01/20/12 10:09, Nikolay Denev wrote:
>> Another thing I've observed is that active/active probably only makes sense if you are accessing single LUN.
>> In my tests where I have 24 LUNS that form 4 vdevs in a single zpool, the highest performance was achieved
>> when I split the active paths among the controllers installed in the server importing the pool. (basically "gmultipath rotate $LUN" in rc.local for half of the paths)
>> Using active/active in this situation resulted in fluctuating performance.
>
> How big was fluctuation? Between speed of one and all paths?
>
> Several active/active devices without knowledge about each other with some probability will send part of requests via the same links, while ZFS itself already does some balancing between vdevs.
>
> --
> Alexander Motin

I will test in a bit and post results.

P.S.: Is there a way to enable/disable active-active on the fly? I'm
currently re-labeling to achieve that.