[RFC] Allow spare's movement only for one metadata type

[RFC] Allow spare's movement only for one metadata type

[Mariusz Tkaczyk]

Hi all,
We are seeing issues related to spares movement managed by mdmonitor in
configurations with IMSM and native arrays because IMSM has some drive specific
checks inside add_to_super_imsm. The spare will be lost if add fails in the
middle of the movement.

For example, IMSM allows to use only one namespace from the nvme drive. If spare
in native array is a second namespace ( by-path link is same for every
namespace, or simply path=* is used) then issue occurs.

I would like to not make mdmonitor more complicated and I don't see the
case when we are configuring spare to be used across many metadata types as
good requirement. For that reason, I would like to propose limiting
mdmonitor spares reassignment functionality to work only across one metadata
type arrays or containers. It means that mdmonitor will be able to move spare
if metadata type is the same for both donor and target.

It deprecates "metadata=" property in POLICY line because there will be no
need to specify metadata if spare can be moved only across one metadata type
arrays/containers.

Thoughts?

Thanks,
Mariusz