ZFS Pool
ZFS storage aggregate: combines multiple vdevs (mirror, RAID-Z, single-disk) into a pool from which datasets allocate. End-to-end checksums detect bit rot, self-healing from mirror/parity.
Snapshots: free (copy-on-write), can be reverted instantly. Compression (LZ4, ZSTD): typically 1.5-3x ratio. Send/recv for incremental backup. RAID-Z1/Z2/Z3 = RAID 5/6/triple parity. ARC = adaptive RAM cache. L2ARC = SSD cache. ZIL = write log on fast SSD. Originally Sun (Solaris), now OpenZFS multiplatform (Linux, FreeBSD, macOS). Classic NAS choice: TrueNAS (FreeNAS fork) builds on ZFS. Storage purists swear by ZFS for data-integrity guarantees. Trade-off: more RAM use (1GB RAM per TB rule of thumb).