Saturday, July 18, 2009

ZFS - A new approach new system

A file system used by OpenSolaris provides simple adminstration, transactional semantics, end-to-end data integrity, and immense scalability.

ZFS Features:
  • Pooled Storage Model
  • Always consistent state
  • Protection from data corruption
  • Live data scrubbing
  • Instantaneous snapshots and clones
  • Fast native back up and restore
  • Higly scalable
  • Buit in compression
  • Simplified adminstration model
Lets see what it means

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 filesystems at all times.

All operations are copy-on-write transactions, so the on-disk state is always valid. There is no need to fsck(1M) a ZFS file system, ever. 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.

ZFS provides unlimited constant-time snapshots and clones. A snapshot is a read-only point-in-time copy of a filesystem, 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.

ZFS backup and restore are powered by snapshots. Any snapshot can generate a full backup, and any pair of snapshots can generate an incremental backup. Incremental backups are so efficient that they can be used for remote replication — e.g. to transmit an incremental update every 10 seconds.

There are in ZFS. You can have as many files as you want; full 64-bit file offsets; unlimited links, directory entries, snapshots, 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.

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