How to scratch/clean an appliance...

I have a v2.5.2 N5220 appliance which I need to decommission, and later re-deploy.

It is/was the 4TB model with no disk shelves.

It was previously configured as a master/media with an MSDP pool (no advanced disk).

I need to ensure, and be absolutely sure, that any old backup data cannot be scavenged.

I'm confortable with re-imageing via IPMI.

So, I'm looking for guidance on how to be sure that no old backup data can be scavenged.

1) Does anyone have any tips/notes/pointers/advice?

2) Do I need to somehow reformat the storage?

3) Or does re-imaging to factory state somehow permanently render all old MSDP data storage disk blocks useless?

4) Is there a documented process?

Thanks.