mirror of
https://git.proxmox.com/git/mirror_zfs.git
synced 2024-11-17 10:01:01 +03:00
870fc32fc9
Most subcommands got their own manpages (e.g. create). Some related commands grouped into a single manpage and symlinks created (e.g. set, get, and inherit). I did this when topics were either too short to warrant their own file or so interrelated that a user would want to refer between commands in the same file. Corrected .Sx internal references to .Xr cross refs; lots of .Sx references from when text was all in zfs.8 needed to be changed to .Xr zfs-$SUBCOMMAND 8 cross references. Divided subcommand list in zfs(8) into sections of related functionality. This required writing new descriptions for some commands. Preserved ".Os Linux", `.Os` macro parsing behavior differs between mandoc from the "BSD" mandoc package (available on Ubuntu) and man from Ubuntu's man-db package, which calls groff to format the manpages. Groff handles the `.Os` macro differently and wrongly, defaulting it to "BSD" in `/usr/share/groff/*/tmac/mdoc/doc-common`, instead of getting the default from `uname`. A future set of changes will introduce build-time preprocessing of manpages for platform-specific documentation and can insert the correct operating system name. Added SEE ALSO sections, the newly-divided zfs-*.8 subcommand man pages needed their own SEE ALSO sections pointing to related subcommands and, in some cases, documentation from other packages (e.g. zfs-share.8). Reviewed-by: Matt Ahrens <matt@delphix.com> Reviewed-by: Kjeld Schouten <kjeld@schouten-lebbing.nl> Reviewed-by: Sean Eric Fagan <sef@ixsystems.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Ross Williams <ross@ross-williams.net> Closes #9559
199 lines
7.2 KiB
Groff
199 lines
7.2 KiB
Groff
.\"
|
|
.\" CDDL HEADER START
|
|
.\"
|
|
.\" The contents of this file are subject to the terms of the
|
|
.\" Common Development and Distribution License (the "License").
|
|
.\" You may not use this file except in compliance with the License.
|
|
.\"
|
|
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
|
|
.\" or http://www.opensolaris.org/os/licensing.
|
|
.\" See the License for the specific language governing permissions
|
|
.\" and limitations under the License.
|
|
.\"
|
|
.\" When distributing Covered Code, include this CDDL HEADER in each
|
|
.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE.
|
|
.\" If applicable, add the following below this CDDL HEADER, with the
|
|
.\" fields enclosed by brackets "[]" replaced with your own identifying
|
|
.\" information: Portions Copyright [yyyy] [name of copyright owner]
|
|
.\"
|
|
.\" CDDL HEADER END
|
|
.\"
|
|
.\"
|
|
.\" Copyright (c) 2009 Sun Microsystems, Inc. All Rights Reserved.
|
|
.\" Copyright 2011 Joshua M. Clulow <josh@sysmgr.org>
|
|
.\" Copyright (c) 2011, 2019 by Delphix. All rights reserved.
|
|
.\" Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
|
|
.\" Copyright (c) 2014, Joyent, Inc. All rights reserved.
|
|
.\" Copyright (c) 2014 by Adam Stevko. All rights reserved.
|
|
.\" Copyright (c) 2014 Integros [integros.com]
|
|
.\" Copyright 2019 Richard Laager. All rights reserved.
|
|
.\" Copyright 2018 Nexenta Systems, Inc.
|
|
.\" Copyright 2019 Joyent, Inc.
|
|
.\"
|
|
.Dd June 30, 2019
|
|
.Dt ZFSCONCEPTS 8
|
|
.Os Linux
|
|
.Sh NAME
|
|
.Nm zfsconcepts
|
|
.Nd An overview of ZFS concepts.
|
|
.Sh DESCRIPTION
|
|
.Ss ZFS File System Hierarchy
|
|
A ZFS storage pool is a logical collection of devices that provide space for
|
|
datasets.
|
|
A storage pool is also the root of the ZFS file system hierarchy.
|
|
.Pp
|
|
The root of the pool can be accessed as a file system, such as mounting and
|
|
unmounting, taking snapshots, and setting properties.
|
|
The physical storage characteristics, however, are managed by the
|
|
.Xr zpool 8
|
|
command.
|
|
.Pp
|
|
See
|
|
.Xr zpool 8
|
|
for more information on creating and administering pools.
|
|
.Ss Snapshots
|
|
A snapshot is a read-only copy of a file system or volume.
|
|
Snapshots can be created extremely quickly, and initially consume no additional
|
|
space within the pool.
|
|
As data within the active dataset changes, the snapshot consumes more data than
|
|
would otherwise be shared with the active dataset.
|
|
.Pp
|
|
Snapshots can have arbitrary names.
|
|
Snapshots of volumes can be cloned or rolled back, visibility is determined
|
|
by the
|
|
.Sy snapdev
|
|
property of the parent volume.
|
|
.Pp
|
|
File system snapshots can be accessed under the
|
|
.Pa .zfs/snapshot
|
|
directory in the root of the file system.
|
|
Snapshots are automatically mounted on demand and may be unmounted at regular
|
|
intervals.
|
|
The visibility of the
|
|
.Pa .zfs
|
|
directory can be controlled by the
|
|
.Sy snapdir
|
|
property.
|
|
.Ss Bookmarks
|
|
A bookmark is like a snapshot, a read-only copy of a file system or volume.
|
|
Bookmarks can be created extremely quickly, compared to snapshots, and they
|
|
consume no additional space within the pool. Bookmarks can also have arbitrary
|
|
names, much like snapshots.
|
|
.Pp
|
|
Unlike snapshots, bookmarks can not be accessed through the filesystem in any
|
|
way. From a storage standpoint a bookmark just provides a way to reference
|
|
when a snapshot was created as a distinct object. Bookmarks are initially
|
|
tied to a snapshot, not the filesystem or volume, and they will survive if the
|
|
snapshot itself is destroyed. Since they are very light weight there's little
|
|
incentive to destroy them.
|
|
.Ss Clones
|
|
A clone is a writable volume or file system whose initial contents are the same
|
|
as another dataset.
|
|
As with snapshots, creating a clone is nearly instantaneous, and initially
|
|
consumes no additional space.
|
|
.Pp
|
|
Clones can only be created from a snapshot.
|
|
When a snapshot is cloned, it creates an implicit dependency between the parent
|
|
and child.
|
|
Even though the clone is created somewhere else in the dataset hierarchy, the
|
|
original snapshot cannot be destroyed as long as a clone exists.
|
|
The
|
|
.Sy origin
|
|
property exposes this dependency, and the
|
|
.Cm destroy
|
|
command lists any such dependencies, if they exist.
|
|
.Pp
|
|
The clone parent-child dependency relationship can be reversed by using the
|
|
.Cm promote
|
|
subcommand.
|
|
This causes the
|
|
.Qq origin
|
|
file system to become a clone of the specified file system, which makes it
|
|
possible to destroy the file system that the clone was created from.
|
|
.Ss "Mount Points"
|
|
Creating a ZFS file system is a simple operation, so the number of file systems
|
|
per system is likely to be numerous.
|
|
To cope with this, ZFS automatically manages mounting and unmounting file
|
|
systems without the need to edit the
|
|
.Pa /etc/fstab
|
|
file.
|
|
All automatically managed file systems are mounted by ZFS at boot time.
|
|
.Pp
|
|
By default, file systems are mounted under
|
|
.Pa /path ,
|
|
where
|
|
.Ar path
|
|
is the name of the file system in the ZFS namespace.
|
|
Directories are created and destroyed as needed.
|
|
.Pp
|
|
A file system can also have a mount point set in the
|
|
.Sy mountpoint
|
|
property.
|
|
This directory is created as needed, and ZFS automatically mounts the file
|
|
system when the
|
|
.Nm zfs Cm mount Fl a
|
|
command is invoked
|
|
.Po without editing
|
|
.Pa /etc/fstab
|
|
.Pc .
|
|
The
|
|
.Sy mountpoint
|
|
property can be inherited, so if
|
|
.Em pool/home
|
|
has a mount point of
|
|
.Pa /export/stuff ,
|
|
then
|
|
.Em pool/home/user
|
|
automatically inherits a mount point of
|
|
.Pa /export/stuff/user .
|
|
.Pp
|
|
A file system
|
|
.Sy mountpoint
|
|
property of
|
|
.Sy none
|
|
prevents the file system from being mounted.
|
|
.Pp
|
|
If needed, ZFS file systems can also be managed with traditional tools
|
|
.Po
|
|
.Nm mount ,
|
|
.Nm umount ,
|
|
.Pa /etc/fstab
|
|
.Pc .
|
|
If a file system's mount point is set to
|
|
.Sy legacy ,
|
|
ZFS makes no attempt to manage the file system, and the administrator is
|
|
responsible for mounting and unmounting the file system. Because pools must
|
|
be imported before a legacy mount can succeed, administrators should ensure
|
|
that legacy mounts are only attempted after the zpool import process
|
|
finishes at boot time. For example, on machines using systemd, the mount
|
|
option
|
|
.Pp
|
|
.Nm x-systemd.requires=zfs-import.target
|
|
.Pp
|
|
will ensure that the zfs-import completes before systemd attempts mounting
|
|
the filesystem. See systemd.mount(5) for details.
|
|
.Ss Deduplication
|
|
Deduplication is the process for removing redundant data at the block level,
|
|
reducing the total amount of data stored. If a file system has the
|
|
.Sy dedup
|
|
property enabled, duplicate data blocks are removed synchronously. The result
|
|
is that only unique data is stored and common components are shared among files.
|
|
.Pp
|
|
Deduplicating data is a very resource-intensive operation. It is generally
|
|
recommended that you have at least 1.25 GiB of RAM per 1 TiB of storage when
|
|
you enable deduplication. Calculating the exact requirement depends heavily
|
|
on the type of data stored in the pool.
|
|
.Pp
|
|
Enabling deduplication on an improperly-designed system can result in
|
|
performance issues (slow IO and administrative operations). It can potentially
|
|
lead to problems importing a pool due to memory exhaustion. Deduplication
|
|
can consume significant processing power (CPU) and memory as well as generate
|
|
additional disk IO.
|
|
.Pp
|
|
Before creating a pool with deduplication enabled, ensure that you have planned
|
|
your hardware requirements appropriately and implemented appropriate recovery
|
|
practices, such as regular backups. As an alternative to deduplication
|
|
consider using
|
|
.Sy compression=on ,
|
|
as a less resource-intensive alternative.
|