ZFS
Also known as: zfs filesystem, zettabyte file system, zfs
ZFS is a copy-on-write file system and volume manager known for end-to-end checksums, snapshots, and built-in block-level deduplication. It pools storage devices together and verifies data integrity on every read.
- ZFS is a copy-on-write file system and volume manager that pools disks and verifies every block with checksums.
- It offers native snapshots, clones, compression, and optional block-level deduplication.
- Common on servers and NAS (OpenZFS, TrueNAS, FreeBSD); phones instead use APFS, ext4, or f2fs.
How ZFS works
ZFS combines a file system and a volume manager. Physical disks are grouped into a *pool* (a `zpool`), and datasets draw space from that shared pool rather than from fixed partitions. It is copy-on-write: instead of overwriting a block in place, ZFS writes a new copy and atomically updates pointers, which keeps the on-disk state always consistent and makes cheap, instant snapshots possible.
Every block stores a checksum in its parent, so ZFS detects silent corruption (bit rot) on read and, when redundancy exists, automatically repairs it — this is the 'end-to-end integrity' it is famous for. Features like compression, snapshots, clones, and scrubbing are native to the file system rather than bolted on.
Deduplication and where you'll meet it
ZFS supports block-level deduplication: identical blocks are stored once and referenced many times, using a hash-indexed dedup table. It is powerful for backup and archival workloads but costly in RAM, so it is used selectively. The same idea — finding identical content and keeping a single copy — is what duplicate-photo and file deduplication features do at the file level on phones.
You typically encounter ZFS on servers, NAS appliances (TrueNAS, illumos, OpenZFS on Linux), and FreeBSD, not on phones. iOS and macOS use APFS, and Android devices use ext4 or f2fs. Understanding ZFS dedup is useful background for how content-addressed storage and duplicate detection conceptually work.