ZFS is about end-to-end integrity, not just redundancy. It stores checksums of data when writing, checks them when reading, and can perform automatic restores from mirror members if mismatches occur. During writes, ZFS generates checksums from blocks in RAM. If a bit flips in memory before the block is written, ZFS will store a checksum matching the corrupted data, breaking the integrity guarantee. That’s why ECC RAM is particularly important for ZFS - without it you risk undermining the filesystem’s end-to-end integrity. Other filesystems usually lack such guarantees.