I have a 6 bay, so yeah that might be a little limiting. I have all my personal stuff backed up to an encrypted cloud mount, the bulk of my storage space is pirated media I could download again, and I have the Synology using SHR so I just plug in a bigger drive, expand the array, then plug in another bigger drive and repeat. Because of duplication sectors you might not benefit as much from that method with just 4 bays. Or if you have enough stuff you can’t feasible push to up to the cloud to give piece of mind during rebuilding I guess.