So a clean install it was. To prepare, I copied a number of setup files to a safe place that wouldn't be overwritten during the install. Files like:
- mdadm.conf, from /etc/mdadm, which had the RAID configuration information.
- xorg.conf, from /etc/X11, which had the custom modeline used to output to my (now ancient) CRT TV.
- ssmtp.conf, from /etc/ssmtp, for email notification in the case of errors.
- apcupsd.conf, from /etc/apcupsd, the setup of the APC UPS monitoring software.
- hardware.conf, from /etc/lirc, used by LIRC to set up the Media Centre remote control.
- the MythTV database password, from /etc/mythtv/config.xml
Not all the files would end up being needed, but I felt safer having them handy, just in case.
The installation process started from a USB stick loaded with the Mythbuntu 12.04 installer, since I don't have an optical drive in it. No room, with three drives already there. I also hooked up a monitor instead of a TV, because that needs extra setup to output to a component connection.
Since there was some left over free space on the SSD, I installed to that, leaving the 10.10 install intact for now. It went remarkably smoothly. One thing I noted was that at the beginning, there is an option to update the installer. I clicked that, and the system seemed to do nothing for quite a while. Opening up a terminal window and running "top" showed that it was in fact doing something, so I waited until it finished. Once done, the installation process could begin. It would have been nice for it to have some sort of indication that it was doing something, though.
Partway through the process, it prompted for what sort of remote control is being used. I selected "Windows Media Center remote", and the thing was set up automatically. Brilliant! Didn't need that LIRC setup file listed above.
To get the system outputting to my TV properly, I just copied the old xorg.conf file to the /etc/X11 directory (I renamed the existing file, in case I needed it again) and rebooted with a sense of hope and anxiety. A minute or so later, the screen came to life! It worked!
The big one, that I was dreading, was getting the RAID array to be seen by the new install. I still consider myself quite the mdadm novice, so I was pleasantly surprised to find that the RAID array was picked up by the new install quite easily - after installing mdadm and lvm2. This command:
sudo mdadm --assemble --scan
was all that was needed for it to scan for any drives, re-assemble the array, and write a new mdadm.conf file. Easy!
Next was seeing if LVM could find the volumes created. Running
sudo lvm pvscan
sudo lvm vgscan
sudo lvm lvscan
detected all the physical volumes, volume groups, and logical volumes, respectively. Mounting the logical volume that held the recordings was successful - I could see them all. Adding the device entry to /etc/fstab seemed to work, eventually. On the first reboot it came up with an error message, mentioning there were serious problems with the mount. Not sure what it was, but a reboot afterwards seemed to make it happy. I had installed xfsprogs, to manage and defragment XFS filesystems; maybe that helped.
Going through some of the MythTV screens brought up some error messages that it couldn't write to the drive - it turned out to be a permissions issue for the files and directories on the array. Entering
sudo chown -R mythtv:mythtv /var/lib/mythtv
changed the ownership back to the mythtv user, and it seemed happy again.
Bringing the previous database over was a painless process as well. I followed the instructions here and here and the new database came over without drama.
So far it all looks good. I may have a tweak of the VDPAU settings to see if playback can be improved any - it looks fine, but the settings have just been carried over from the previous 0.23 version. Things may have changed in the current 0.25 release.
Now that the system is updated to 12.04, which is a Long Term Support (LTS) release of Ubuntu, I won't be caught out with an obsolete version after 18 months like I was with 10.10.
As a side note, one of the main reasons for moving to 64-bit was because the Zotac IONITX-A-U motherboard, with an Atom 330, was only showing 3GB of RAM installed, even though I had two, 2GB sticks in there. I thought this was a 32 bit software issue. After installing the 64-bit OS, the free memory remained the same. Even in the BIOS, it only reported 3072MB. Strange. A bit of searching around revealed this thread on Zotac's supprt forums. As it turns out, if 4GB is installed, 512MB is reserved for system use, and then there is the amount used by the onboard Nvidia ION graphics - which I had set to the maximum allowed 512MB. So only 3GB visible. It's OK, it still runs fine, but it would have been nice to be able to use a little extra.