Mittlerweile hat sich der Support von Backblaze geantwortet und schiebt die Kugel an Arq oder die Hardware zurück :-)

Hello Michael,
Based on the errors reported in the log, it appears the Arq software was having trouble reading the 4 specified files due to input/output errors. This typically indicates an issue with the local storage device, controller, or some similar issue, but Arq support would likely have the best information as it's their software and log files.
Regards,
Christopher

Na, mal sehen, wie sich das so entwickelt.
Der Händler baut mir natürlich gerne eine neue FusionDrive ein, keine Frage.
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Scheiß der Hund drauf.