Re: [dm-devel] 2.6.10-rc1-udm1: multipath work in progress

[Alasdair G Kergon <agk redhat com>]

On Tue, Nov 02, 2004 at 03:51:03PM +0100, Stefan Bader wrote:
> Personally I would rather see path information moving into the path 
> selector

We need some concrete examples of what information is missing and
how other sorts of path selectors would benefit from it.

> There are even some fields and functions in dm-mpath.c 
> (current_count) that are rather specific to a selector. 

That's a generic optimisation - you normally don't want to be 
recalculating which path to use for every single I/O - choose
a path, then send the next X I/O down it before reassessing
which to use.

> For path selectors: what about per selector arguments?

Probably, but first we need some concrete examples of arguments that
can't be per-path.

> For example the round-robin could take the number of io operations
> before switching to the next path:
> round-robin 1 1000 2 1 7:1 1 7:2

It already does, as a more-flexible per-path argument.

Alasdair
-- 
agk redhat com