RAID1 arrays not starting with missing drive

[Rich Carreiro]

I've just installed a Gusty system as LVM-over-RAID1.

I have two RAID1 devices -- /dev/md0 which is /boot (and
does NOT use LVM) and is made up of /dev/sda2 and /dev/sdb2,
and /dev/md1 which has LVM (and the rest of the system) over it
and is made up of /dev/sda3 and /dev/sdb3.

I've grub'd both /dev/sda and /dev/sdb, and as long as
both drives are plugged in, I can boot from either drive
and everything works and is happy.

However...

When I try to boot with a drive removed (for testing purposes),
grub comes up fine and the system begins to boot, but it appears
that the arrays will not start, which means there's no root filesystem
available and everything grinds to a halt.  This doesn't seem right.
Given the nature of RAID1, the arrays darn well should start up even
with a missing drive.

The boot output when the drive is missing has:
   md: md0 stopped
   md: bind <sda2>
   md: md1 stopped
   md: md0 stopped
   md: unbind <sda2>
   md: export_rdev(sda2)
   md: bind <sda2>
   md: md1 stopped
   md: bind <sda3>
and then everything grinds to a halt.

When both drives are present, this section goes:
   md: md0 stopped.
   md: unbind<sdb2>
   md: export_rdev(sdb2)
   md: bind<sdb2>
   md: bind<sda2>
   raid1: raid set md0 active with 2 out of 2 mirrors
   md: md1 stopped.
   md: bind<sdb3>
   md: bind<sda3>
   raid1: raid set md1 active with 2 out of 2 mirrors

So why won't the arrays start up when a drive is missing (it doesn't
matter which drive is the missing one)?

--
Rich Carreiro                            rlcarr at rlcarr.com