Sometime early last year, one of the hard drives died. But, I had been meaning to upgrade, so I figured I'd upgrade both hard drives and reinstall. So I backed up to a new machine and started plugging away, but I couldn't convince Ubuntu to boot from a RAID partition.
Time passes. I keep thinking about at least plugging in one of the new hard drives, but don't.
So, a year after the initial attempt, I go through the install process and decide to just have an un-RAIDed /boot (with a manual /boot-backup.) But one of the replacement hard drives has gone bad and fails during the install process. After verifying that it's really the drive at fault, off to Micro Center for a replacement.
Even though the drives are now happy, the new installation doesn't work. On boot Linux decided that the RAID group should be /dev/sda and /dev/sdb instead of /dev/sda6 and /dev/sdb6.
Much hair-pulling later, the problem seems to be that mdadm find the /dev/sda6 superblock (the partition) when it probes /dev/sda (the whole device). I still have no idea why. Also scanning /proc/partitions seems to be flaky because the partitions are not always listed. Sometimes I would get /dev/sda pasted together with /dev/sdb6. Googling turned up all sorts of kinda-related symptoms, which led me to the conclusion that this just Does Not Work Well.
The fix is to tell mdadm, in its configuration file (in the initrd!), to just scan the two partitions of interest. This seems to allow my system to boot, but of course bypasses all the helpful features that are meant to keep the system alive even if the drives are swapped or the controller reorders them or you add a new disk or whatever. (I am feeling better all the time about our decision not to use native MD for the Tintri filesystem RAID.)
Next up: why the heck doesn't my X windows display work?
Periodically the screen blanks. Even at 1024x768 @60Hz it occasionally flakes out. Still not sure whether this is the Dell display firmware crapping out, or my ancient Radeon video card.
The default 1280x1024 which Ubuntu picked was a complete disaster. The monitor is capable of 1920x1200 @60Hz and I can see its mode line listed in X's log. But trying to use that configuration results in a screen full of garbage, even though I know the two pieces of hardware are capable of it. Maybe the X.org driver just isn't as good as the old XFree86 one?