On Wed, May 15, 2013 at 8:41 PM, NeilBrown [off-list ref] wrote:

The problem with doing this is that it is potentially an API change.
It is unlikely but possible that some script depends on the current meaning
of the number.

Also it would result in spares being reported as e.g.
     sda1[-1]S
as 'raid_disk' for a spare is '-1'.

Excellent points. Yes it would be a sort of an API change which would
not be good for people who depend on it to act that way. That is sort
of how I ended up "caring so much" about it in the first place. 0.90
metadata behaved one way and now 1.X behaves differently so I need to
update some tools to take that into account. Before I updated the
tools I wanted to make sure it wasn't a "bug" and something that you
wanted to fix. If it was then I would possibly try to pull in the
kernel patch rather than change the tools.

My leaning is to not worry too much about /proc/mdstat, but instead add a
"--status" option to "mdadm" which prints out a summary similar
to /proc/mdstat, but more coherent and less full of noise.

This looks nice but I wouldn't discount the value of /proc/mdstat. If
monitoring tools check the status of raid often then I would rather
them use file I/O of a file maintained by the kernel rather than
running a command each time and parsing output.

Thanks for collaborating with me on this. I'll update my tools.

Dusty Mabe