Re: dm-multipath: Accept failed paths for multipath maps

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Jul 17 2014 at  8:29pm -0400,
John Utz <John.Utz@wdc.com> wrote:

> What are the release testing criteria for things like this? From a
> hand wavy perspective i am sure that the meta-requirement is 'don't
> break anything'. but how is a new release proven to not break
> anything?

Red Hat and other vendors have their own testbeds and harnesses for
testing dm-multipath.  But we really could benefit from more open
exchange and collaboration of a multipath test harness.

Had I actually tested the patches I pointed to it'd have blown up
pretty solidly, I realized something like this was needed:
http://git.kernel.org/cgit/linux/kernel/git/snitzer/linux.git/commit/?h=throwaway-dm-mpath-placeholder-devs&id=77d1130e602a399ed1451edd7e91044fe9225fb6

Anyway, I really don't like that 'place-holder device' approach.. way
too hackish (both my code and Hannes').  It is an elaborate workaround
rather than a proper solution.  I'm hopeful Bryn takes this multipath
problem under his wing and fixes it for real ;)

> fer instance, does anybody create dm devices, format them with XFS and
> then run xfstests against them?

We routinely use XFS and ext4 with git to generate load.  But not
xfstests... that may be useful.

> or some other formalized regimen?
> 
> or is it all kinda ad-hoc?

We have the device-mapper-test-suite (dmts) for testing various DM
targets (mainly dm-thinp and dm-cache), see:
https://github.com/jthornber/device-mapper-test-suite

I added basic support for dm-crypt to dmts; but it needs serious
expanding for it to be useful.. luckily the cryptsetup userspace code
has dm-crypt tests.

Also, the lvm2 testsuite is another major resource that is used for
testing the wide range of DM targets.