Hi @afitzek, the result looks actually bad, basically each and every block is bad:
$ sudo badblocks -nvs /dev/sdb
Checking for bad blocks in non-destructive read-write mode
From block 0 to 15645695
Checking for bad blocks (non-destructive read-write test)
Testing with random pattern: 0
...
Pass completed, 15645696 bad blocks found. (0/0/15645696 errors)