hi wolfy, this is a good question:
as far as i know, there should still be a way to do that via support, even if out of support/eol (though it would involve a 1-time paid support ticket, and maybe that was not what you were looking for at the time)
having said that… i am not yet aware of a failsafe (tried and tested) method, of doing this manually…
- for example i do not know (by way of not having tried), to power all off, and put a drive into a standalone caddy, to run an external separate tool, such as a full surface scanner which must be non-destructive, and then putting that drive back in still while drobo power is off, and then powering back up and everything would be still working?
i have used suface scanners such as datalifeguard from WD, which is free, but only on drives that either failed in some way, or on new drives before i put them into a drobo.
the only industry standard hard drive tool that seems to get a lot of praise, is spinrite, but again that needs to be purchased, and i dont think it supports drives larger than a certain amount (possibly 2tb), and i have not heard of this being successfully used in a drobo.
(however the spinrite tool really does interest me, and i think there is a possible future in merging spinrite with drobo)
i am also always open to learning new things if anyone has any more tools or info on ways forward for this topic or others in general