Earlier quoted context omitted.
> Then you contact support, appoint disk change, you first deactivate disk on raid (save geometry etc), they replace disk and then you rebuild raid in new disk. That's it. I imagine this would take time, right? Like not 5 minutes, but maybe 3 hours top? So, if I pretend to run a saas (that shouldn't be down more than 1h/day), then renting only 1 dedicated server could be qualified as "risky"?
I'm not sure what "deactivating RAID" means. They will all be hot-swap disks. You remove the old disk and slide in the new one (or in this case, tell them to do it). The RAID system rebuilds the array in the background over the next few hours. During that time you will lose data if it's RAID 5 and another disk fails.
mdadm --manage --remove
so your machine doesn't have a fit when the disk is detached. Or equivalent.