My Rock64 has two discs attached to it, the first (Boss) holds all of my data and back ups, the second (Slave) is a scheduled rsync copy of Boss that runs at 02:30 daily.
Last night both discs spontaneously unmounted at around 02:39 (the time of a system email). Any idea why this might happen?
This scheduled job has run largely unchanged for the past 6 months. The only modification is I upgraded Slave two days ago and enabled write cache. I left it copying Boss during the day yesterday.
I got a "sending incremental file list" message at 02:30 which indicated that Slave was an exact copy of Boss.
For the record I am getting several daily CRON-APT messages about "Failed to fetch http://security.debian.org/dists/jessie/updates/InRelease Unable to find expected entry 'main/binary-arm64/Packages' in Release file".