My nas uses zfs for the storage drives, this allows for on the fly filesystem creation, no need for partitions, error checking, and software raid.
However it did mean I had to use freebsd, which is weird compared to debian. Now debian/kfreebsd is out I'll switch at some point.
Limitations: you can't increase the number of drives in a raidz, and no built in filesystem encryption. Also I once encounted a bug that stopped me accessing snapshots until I rebooted. Also no built in encryption.
Level 1: Fault tolerance: zfs software raid
Level 2: Old versions of files: zfs snapshots
Level 3: Disaster recovery: zfs send/receive snapshots, to remote computer/external drive
Level 4: Archive: same as level 3
ZFS snapshots are files that can be encrypted, copied etc. Also they can be converted back into a filesystem.
You can also do incremental snapshot backups, and these can be merged with zfs send, although not currently with encryption.