The USB freeze up problem isn’t happening any more. I don’t know exactly what fixed it, but I ran the SEATools long test on it, ran fsck on it, plugged it into a different USB port in a different cradle. Possibly coincidentally, I was having another problem with not being able to log off or authenticate in the software update program, and one suggestion I found on-line was to install a particular “KDE extras” package which seems to have cured those problems.
The replacement disk for the one that came with errors arrived, and a quick fdisk and mdadm /dev/md128 --add /dev/sdb1 and it rebuilt overnight and everything looks ship shape and Bristol fashion. Hopefully I won’t be getting any more “degraded array” emails, and hopefully when I reboot it, it won’t stop at the “initramfs” prompt waiting for me to fix whatever is wrong.
Oh, I also fixed a problem with Google Chrome occassionally freezing. I looked in my .xsession-errors file and it was filling up with messages that said “ALSA lib pcm_dmix.c:957:(snd_pcm_dmix_open) The dmix plugin supports only playback stream”. Googling that found that I had to start Chrome with google-chrome --disable-bundled-ppapi-flash to disable the built-in Flash. Fortunately when you do that it uses the Adobe Flash plugin that was installed for FireFox so everything keeps working as before.
I’ve got to say, I’m really loving KDE. It really works well and looks good.