What is ZFS?

ZFS is a new kind of file system that provides simple administration, transactional semantics,
 end-to-end data integrity, and immense scalability. ZFS is not an incremental improvement
 to existing technology; it is a fundamentally new approach to data management.
We've blown away 20 years of obsolete assumptions, eliminated complexity at the
 source, and created a storage system that's actually a pleasure to use.

ZFS presents a pooled storage model that completely eliminates the concept
 of volumes and the associated problems of partitions, provisioning, wasted
bandwidth and stranded storage. Thousands of file systems can draw from a
 common storage pool, each one consuming only as much space as it actually needs.
 The combined I/O bandwidth of all devices in the pool is available to all file systems at all times.

All operations are copy-on-write transactions, so the on-disk state is always valid.
 Every block is checksummed to prevent silent data corruption, and the data is
 self-healing in replicated (mirrored or RAID) configurations. If one copy is damaged,
ZFS detects it and uses another copy to repair it.

ZFS introduces a new data replication model called RAID-Z. It is similar to RAID-5
 but uses variable stripe width to eliminate the RAID-5 write hole (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 — the best part —
 no need for NVRAM in hardware. ZFS loves cheap disks.

But cheap disks can fail, so ZFS provides disk scrubbing. Similar to ECC memory scrubbing,
 all data is read to detect latent errors while they're still correctable.
A scrub traverses the entire storage pool to read every data block,
 validates it against its 256-bit checksum, and repairs it if necessary.
All this happens while the storage pool is live and in use.

ZFS has a pipelined I/O engine, similar in concept to CPU pipelines.
The pipeline operates on I/O dependency graphs and provides scoreboarding, priority,
 deadline scheduling, out-of-order issue and I/O aggregation. I/O loads that
 bring other file systems to their knees are handled with ease by the ZFS I/O pipeline.

ZFS provides 2 ⁶⁴ constant-time snapshots and clones. A snapshot is a read-only
 point-in-time copy of a file system, while a clone is a writable copy of a snapshot.
 Clones provide an extremely space-efficient way to store many copies of
mostly-shared data such as workspaces, software installations, and diskless clients.

You snapshot a ZFS file system, but you can also create incremental snapshots.
Incremental snapshots are so efficient that they can be used for remote replication,
 such as transmitting an incremental update every 10 seconds.

There are no arbitrary limits in ZFS. You can have as many files as you want: full
64-bit file offsets, unlimited links, directory entries, and so on.

ZFS provides built-in compression. In addition to reducing space usage by 2-3x,
compression also reduces the amount of I/O by 2-3x. For this reason, enabling
 compression actually makes some workloads go faster.

In addition to file systems, ZFS storage pools can provide volumes for applications
 that need raw-device semantics. ZFS volumes can be used as swap devices,
 for example. And if you enable compression on a swap volume, you now have
 compressed virtual memory.

ZFS administration is both simple and powerful. Please see the zpool(1M) and
zfs(1M) man pages for more information — and be sure to check out the Getting Started
 section for a whirlwind tour.

ZFS is already quite snappy on most workloads — and we're just getting started.