I plan to have one master server including several HDDs (for RAID5, probably all homogeneous with 4TB each), and one remote slave server containing only one big capacity HDD, or a bunch of disks not necessarily all the same capacity. These 2 servers would have encrypted disks. It would be for running web/mail/media/git services etc, hosting software ISOs and video files larger than 4GB, and I'd have to set different rights/quotas for my family members. Hot swap/addition of a disk would be appreciated (don't know if this rather lies into OS choice though)
(I remember having corrupted an external drive and all its data, probably either or both because conflicts when alternating plugs into linux ext4 and windows ntfs machines, and letting it plugged when turning machines on sleep mode/hibernation.)
1) Assuming common filesystem for windows 10 is NTFS and for debian/xubuntu/arch 2020 is ext4 (idk what it is for macOS iOS and Android), what would be the optimal file system for the servers please, if any? If there isn't such, in what filesystems should I reinstall my different client machines for compatibility at least between each of them and the server (at most between any combination of 2 of them)?
2) Do the softwares pushing incremental backups that are installed on the clients have to be considered for this choice? Or is it usually only the servers which pulls everything anywhere?
3) Raid5 implies one disk crash tolerance, but are there actually ways to be notified of such crash ? Otherwise I'd rather choose other RAIDS with more tolerance if I don't have access to the server for a while.