ZFS

In the previous article , we explored Btrfs—a copy-on-write filesystem built around a single kind of B-tree, where every file, extent, checksum and chunk mapping lives as a tagged item in some tree, and snapshots fall out of the reference-counted extent design. Btrfs took a lot of inspiration from an older system that pioneered most of these ideas: ZFS. ZFS started life at Sun Microsystems in the mid-2000s and now lives on as OpenZFS, ported to Linux, FreeBSD, illumos, and macOS. From the outside it solves the same problems as Btrfs—pooled storage, copy-on-write, snapshots, checksums, integrated RAID—but the shape underneath is genuinely different. Where Btrfs leaned on one universal B-tree node format and a single key shape, ZFS leans on something else entirely: a 128-byte block pointer that fully describes the block it points to, and a strict three-layer architecture stacked on top of it.