Hardware Can I migrate from RAID1 to RAID10?

[DiscostewSM]

First time NAS user who plans to buy some HDDs during Black Friday. Initially I just want to have 2 HDDs in a RAID1 setup, but down the road I might want to expand to another 2 drives. I have the DS918+ which only has 4 bays (don't plan to buy the expansion module for 5 more bays). RAID5/6 (as SHR-1 and SHR-2 with Synology) seem too risky by comparison because of the rebuilding as if I lose a drive during rebuilding, then all data is lost.