Am Thu, 05 Mar 2015 15:00:18 -0500
schrieb Phil Turmel [off-list ref]:

It has to stay there to give errors to the upper layers that are still
hooked to it.  When they are administratively "unhooked", aka
unmounted or disassociated with mdadm --remove.

Or, quite possibly, the device is plugged back in, at which point the
device name is there for it (as long as you use the same port, of
course).  In which case the filesystem may very well resume
successfully.

From reading this it makes sense that the md device stays there, just
as the the physical device nodes. (to give errors, and to recover)

However, as I understood this thread, md does not seem to inform upper
layers or the user (even not through its own --monitor?) properly.
To me, marking the last disk within an array as failed (*within* the
array) just seems to make more sense, so /proc/mdstat actually
iforms about the md error state (and the md device returning errors on
access).

Regards,
Chris