Hello, everybody,
I already posted this in the german forum, but maybe it helps here too.
Unfortunately I also made the mistake to update from 6.2 to 6.2.1 and the system was no longer available. But after some trial and error I found a solution:
I removed every single one of the hard disks of the raid system and connected them to the PC with a USB adapter. There I used the free partitioning tool Minitool Partition Wizzard to run a wipe on the 2.37GB partition (overwriting the partition with zeros). This is the system partition of the DSM.
Caution: You are not allowed to do anything on the other partitions and the installation order of the hard disks must also be observed.
Then I created a new 1.03 Bootloader USB stick and started the system. The Synology Finder found the DSM and didn't show any installation. I then manually installed the DSM_DS3617xs_23739.pat file.
After the first start the old volume was detected error free. All data was still there. Only the packages had to be reinstalled.
I think the solution will work with all versions.