A Solaris file system that uses storage pools to manage physical storage. The ZFS pooled storage model eliminates the concept of volumes and the associated problems of partitions, provisioning and stranded storage by enabling thousands of file systems to draw from a common storage pool, using only as much space as it actually needs. ZFS also uses RAID-Z, a data replication model that is similar to RAID-5 but uses variable stripe width to eliminate the RAID-5 write hole-that is stripe corruption due to loss of power between data and parity updates. All RAID-Z writes are full-stripe writes. There's no read-modify-write tax, no write hole, and no need for NVRAM in hardware.
According to the FAQ posted on OpenSolaris.org, originally, ZFS was an acronym for "Zettabyte File System." The largest SI prefix that the developers liked was 'zetta', and since ZFS is a 128-bit file system, the name was a reference to the fact that ZFS can store 256 quadrillion zettabytes (where each ZB is 270 bytes). Over time, ZFS gained a lot more features besides 128-bit capacity, such as rock-solid data integrity, easy administration, and a simplified model for managing your data.
ZFS is open-source software that is licensed under the Common Development and Distribution License (CDDL).