Text 14809, 86 rader
Skriven 2006-12-18 18:57:18 av mike (1:379/45)
  Kommentar till text 14806 av mike (1:379/45)
Ärende: Re: ZFS on OS-X?
========================
From: mike <mike@barkto.com>

On Mon, 18 Dec 2006 17:26:26 -0500, mike <mike@barkto.com> wrote:

[snip]
>Some more info:


Still more info:
http://opensolaris.org/os/community/zfs/whatis/

===
ZFS is a new kind of filesystem 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 filesystems 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 filesystem, 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 will
detect it and use 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. Like ECC memory
scrubbing, the idea is to read all data to detect latent errors while they're
still correctable. A scrub traverses the entire storage pool to read every copy
of every block, validate it against its 256-bit checksum, and repair 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 filesystems to their knees are handled with ease by the
ZFS I/O pipeline.

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 no arbitrary limits 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 filesystems, 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.
===

 /m

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