(OT) problem with unknown software

[ghe <ghe@slsware.net>]

For several days, I've been getting email from myself, with no date,
title:

Problem: /dev/sdd is UNKNOWN at 2017-05-18 11:56:30 from sbox
(<correct IP>)

The body:

/dev/sdd () is Unavailable

The Received: header:

Received: from localhost (sbox.slsware.net [<correct IP>])
	by srv.slsware.net (srv.slsware.net) with ESMTP id 5701F2C06E2
	for <ghe@slsware.net>; Thu, 18 May 2017 11:56:29 -0600 (MDT)

#1: There is, for sure, a /dev/sdd on the machine (it's half of md1, the
number 2 RAID1 array), and

#2: I can't remember what I installed (with Aptitude, almost certainly)
that's doing this.

Does anyone know what piece of bent software can find /dev/sda, b, and
c, but not sdd? Or what I did to break it?

-- 
Glenn English