I can confirm this report. I occasionally do what the original reporter does: replace an entire set of disks on a live server using mdadm --fail / mdadm --remove / [physical hot swap] / mdadm --add / grub-install, and the identical problem happened to me.
In my case the disks are a three-disk RAID 1 array rather than RAID 10, and I partitioned them with "parted" rather than using "dd". I replaced the first two and grub-install worked with no trouble: # grub-install /dev/sdc # grub-install /dev/sdb But the third gave me: # grub-install /dev/sda /usr/sbin/grub-probe: error: no such disk. Auto-detection of a filesystem of /dev/md0 failed. # grub-install --recheck /dev/sda /usr/sbin/grub-probe: error: no such disk. Auto-detection of a filesystem of /dev/md0 failed. ... with the other symptoms identical. To my astonishment, running this: # mdadm --examine /dev/sda2 ... fixed it; "grub-install /dev/sda" then works without errors. Clearly "mdadm --examine" has a mysterious helpful side-effect, the nature of which is puzzling. However, I can't reproduce the original problem on demand; this has happened to me only once when doing this on about half a dozen physically identical (in terms of hardware) servers. -- Robert L Mathews
