I am happy to be able to tell you that I have solved my problem.
First of all thanks to Synology for rapidly sending us a new "100W PSU". Unfortunately that didn't solve our problem, but you don't know that until afterwards.
Secondly, thanks to the tips above to sanitize the disk(s). I let the DBAN software have a go at disk one (five hours) and it came out with just as many green lights as before (all green in the WD-tool).
Then I figured that (at least in my very case) I either have a problem with disk 1 or I don't have any problems at all with any disk. I voted for the latter. So I skipped sanitizing the other three disks and instead prepared for restoring the complete volume from scratch:
1) Backed up all system-settings.
2) Had a fresh USB-backup done to another USB-disk (in case my standard USB-disk would somehow be faulty).
3) Removed the existing "volume1"
4) created a new volume
5) imported the old settings (users, permissions)
The only problem arose when I tried to restore all the data. I was not impressed with the built-in "file station". Ok, it does not share the same layout as the usual admin-pages, but had it worked correctly I could have accepted this. I tried to restore ONE folder and it was hanging. I also was unable to mark all folders for restoration in one go. Strange.
Luckily we nowadays have an officially supported telnet- and SSH-patch to the cubestations, so I simply logged in with SSH and issued a
Code: Select all
mkdir /volume1/tmp/ ;
cp -R /volumeUSB1/usbbackup/* /volume1/tmp/
and finally "mv" the various folders to their proper locations under my new /volume1".
Thanks again to this forum for supporting me.