As far as data in concerned it's with your disks.
- UPDATE: DSM loads boot modules and some specific information to RAM. Hence you are able to boot or use the synology assistant and receive the OS version etc when not disks are inserted. To be clear and safe I would recommend resetting the synology box using the steps below.
Think of the DSM as the operating system that lives on the memory chips inside your machine regardless of your disks. So things like network setup user accounts, RAID config and the rest are stored here.
This is to enable you to replace drives without losing the Operating System.
Best way to make ultimately sure is to reset to factory settings your DSM, which you probably have done already by the sounds of it. But just in case use this guide:
For models installed with DSM 2.2-0941 and onward
- The RESET button on the Synology product has the following functions.
- To restore the "admin" account to default value.
- To reset the UI management port to 5000/5001. To reset IP, DNS, gateway, and other net interfaces to DHCP. To disable PPPoE.
- To disable auto block.
- To disable firewall rules.
- To unmount encrypted folders and disable Mount automatically on startup.
To remove high-availability cluster.
Please note that the hard drive will not be formatted, so you don't have to worry about losing data.
Guide:
https://www.synology.com/en-uk/knowledgebase/DSM/tutorial/General/How_to_reset_your_Synology_NAS