Thanks To-P and Al-S,

I ran another Volume System Check on the Areca Controller and it reported a read-error on one drive 7 times during the check. I replaced the disk with a fresh one and for now all seems to be good.

If this really solves the problem it would be strange the whole systems hangs just because of a faulty drive (the RAID controller should take care of that).

Firmware is 1.49 (which is the latest for the ARC-1261)