Someone asked a question yesterday about the 5366 and after a fairly extensive search I found absolutely nothing. Maybe look at the specs for a previous model to get an idea what capacity drives you can plug in. If you do find something let us know as I am sure there will be more questions on this device in the future,
So far I can tell you for fact. The modem has a usb c connection which means for most hard drives you will need an adapter. I'm getting it installed tommorow afternoon. I hope It's going to support my hard drive.
Not an answer, but consider a NAS. These have external USB connections but make content available across your network. Good redundancy options too with things like mirror raid.
This seems like a very comprehensive reply:
Not much on the Sagemcom site: