Thanks for that. At the moment I'm restarting the database server every morning as soon as I wake up, which is clearly unsustainable (especially if I want to have a lie in at the weekend!). On Sunday morning I was up early enough to watch it all go down, in real time, which was informative.
Despite my efforts to prevent it, several automated jobs kicked in while the database dump was ongoing, including the 5-minutely homepage refresh. Each of these needs disk and database access, while the database is both locked out and hammering the disk. What
should happen is that the automated jobs either exit immediately (for the 5-minute job) or sleep until the backup is complete, and that didn't happen. I'm investigating that at the moment.
Once things are stable again, I can look at eliminating the nightly downtime for backup, but that's a significantly harder problem.
My friend and I applied for airline jobs in Australia, but they didn't Qantas.