Re: dm core patches

[Joe Thornber <thornber@redhat.com>]

On Thu, Feb 12, 2004 at 07:51:45PM +0100, Lars Marowsky-Bree wrote:
> I checked the archives, but I couldn't find anything really 'in flux'.
> Your priority based approach seems just fine to me.
> 
> What is still missing? This is really a killer feature for 2.6. Any help
> I can offer?

I think the main concern now is over the testing of paths.  Sending an
io down an inactive path can be very expensive for some hardware
configurations.  So I'm considering changing a couple of things:

- Only ever send io to 1 priority group at a time (even test ios).
  To test the lower priority groups we'd have to periodically switch to
  them and use them for a bit for both test io and proper io.

- For some hardware there are better ways of testing the path than
  sending the test io.  Should the drivers expose a test function ?
  In the absence of this we'd fallback to the test io method.

The other thing we need is to try and get the drivers to deferentiate
between a media error and a path error, so that media errors get
reported up quickly and don't cause false path failures.  This is
possibly an area that you could help with ?

- Joe