RAID1 on Ubuntu: Array fails to assemble on boot

A few days after getting my RAID1 devices running smoothly, I rebooted to apply some package updates, and the boot process stopped due to an e2fsck problem. Again.

e2fsck 1.41.4 (27-Jan-2009)
e2fsck: Invalid argument while trying to open /dev/md0

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>

RAID1 problems: access beyond end of device

After getting my RAID1 arrays running on my Ubuntu server, I moved the case back into the crawlspace under the stairs and powered it on. Later I started up an SSH but the connection was denied. Great; I had to lug the thing back into the office to connect a monitor and keyboard. The boot process stopped due to a failed fsck with output similar to the following:

e2fsck 1.41.4 (27-Jan-2009)
The filesystem size (according to the superblock) is 244190000 blocks
The physical size of the device is 244189984 blocks
Either the superblock or the partition table is likely to be corrupt!

Setting up RAID1 in Ubuntu

My Ubuntu server has been running for a few years with half a terabyte of photos, TV episodes, and MP3s served up by Samba and ProFTPD. When Glenn, a friend at work, let me know that Newegg had a coupon code bringing the low-power WD Green HDs of the 1TB variety under $80, I decided to buy a couple to upgrade storage and insure against disk failure for my precious audiobooks.
I love Newegg, but somehow neither drive would be recognized by hierax's BIOS nor my desktop's, so back they went. It cost me another $10 to send them back, but when I finally got a couple of good replacement drives, I setup the RAID1 array. It was a lot easier than I expected thanks to mdadm.