fix #3884: Add section for kernel samepage merging

[pve-docs.git] / vzdump.adoc

[[chapter_vzdump]]
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vzdump(1)
=========
:pve-toplevel:

NAME
----

vzdump - Backup Utility for VMs and Containers 


SYNOPSIS
--------

include::vzdump.1-synopsis.adoc[]


DESCRIPTION
-----------
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Backup and Restore
==================
:pve-toplevel:
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Backups are a requirement for any sensible IT deployment, and {pve}
provides a fully integrated solution, using the capabilities of each
storage and each guest system type. This allows the system
administrator to fine tune via the `mode` option between consistency
of the backups and downtime of the guest system.

{pve} backups are always full backups - containing the VM/CT
configuration and all data.  Backups can be started via the GUI or via
the `vzdump` command line tool.

.Backup Storage

Before a backup can run, a backup storage must be defined. Refer to
the Storage documentation on how to add a storage. A backup storage
must be a file level storage, as backups are stored as regular files.
In most situations, using a NFS server is a good way to store backups.
You can save those backups later to a tape drive, for off-site
archiving.

.Scheduled Backup

Backup jobs can be scheduled so that they are executed automatically
on specific days and times, for selectable nodes and guest systems.
Configuration of scheduled backups is done at the Datacenter level in
the GUI, which will generate a job entry in /etc/pve/jobs.cfg, which
will in turn be parsed and executed by the `pvescheduler` daemon.
These jobs use the xref:chapter_calendar_events[calendar events] for
defining the schedule.

Backup modes
------------

There are several ways to provide consistency (option `mode`), 
depending on the guest type.

.Backup modes for VMs:

`stop` mode::

This mode provides the highest consistency of the backup, at the cost
of a short downtime in the VM operation. It works by executing an
orderly shutdown of the VM, and then runs a background Qemu process to
backup the VM data. After the backup is started, the VM goes to full
operation mode if it was previously running. Consistency is guaranteed
by using the live backup feature.

`suspend` mode::

This mode is provided for compatibility reason, and suspends the VM
before calling the `snapshot` mode. Since suspending the VM results in
a longer downtime and does not necessarily improve the data
consistency, the use of the `snapshot` mode is recommended instead.

`snapshot` mode::

This mode provides the lowest operation downtime, at the cost of a
small inconsistency risk. It works by performing a {pve} live
backup, in which data blocks are copied while the VM is running. If the
guest agent is enabled (`agent: 1`) and running, it calls
`guest-fsfreeze-freeze` and `guest-fsfreeze-thaw` to improve
consistency.

A technical overview of the {pve} live backup for QemuServer can
be found online
https://git.proxmox.com/?p=pve-qemu.git;a=blob_plain;f=backup.txt[here].

NOTE: {pve} live backup provides snapshot-like semantics on any
storage type. It does not require that the underlying storage supports
snapshots. Also please note that since the backups are done via 
a background Qemu process, a stopped VM will appear as running for a 
short amount of time while the VM disks are being read by Qemu.
However the VM itself is not booted, only its disk(s) are read.

.Backup modes for Containers:

`stop` mode::

Stop the container for the duration of the backup. This potentially
results in a very long downtime.

`suspend` mode::

This mode uses rsync to copy the container data to a temporary
location (see option `--tmpdir`). Then the container is suspended and
a second rsync copies changed files. After that, the container is
started (resumed) again. This results in minimal downtime, but needs
additional space to hold the container copy.
+
When the container is on a local file system and the target storage of
the backup is an NFS/CIFS server, you should set `--tmpdir` to reside on a
local file system too, as this will result in a many fold performance
improvement.  Use of a local `tmpdir` is also required if you want to
backup a local container using ACLs in suspend mode if the backup
storage is an NFS server.

`snapshot` mode::

This mode uses the snapshotting facilities of the underlying
storage. First, the container will be suspended to ensure data consistency.
A temporary snapshot of the container's volumes will be made and the
snapshot content will be archived in a tar file. Finally, the temporary
snapshot is deleted again.

NOTE: `snapshot` mode requires that all backed up volumes are on a storage that
supports snapshots. Using the `backup=no` mount point option individual volumes
can be excluded from the backup (and thus this requirement).

// see PVE::VZDump::LXC::prepare()
NOTE: By default additional mount points besides the Root Disk mount point are
not included in backups. For volume mount points you can set the *Backup* option
to include the mount point in the backup. Device and bind mounts are never
backed up as their content is managed outside the {pve} storage library.

Backup File Names
-----------------

Newer versions of vzdump encode the guest type and the
backup time into the filename, for example

 vzdump-lxc-105-2009_10_09-11_04_43.tar

That way it is possible to store several backup in the same directory. You can
limit the number of backups that are kept with various retention options, see
the xref:vzdump_retention[Backup Retention] section below.

Backup File Compression
-----------------------

The backup file can be compressed with one of the following algorithms: `lzo`
footnote:[Lempel–Ziv–Oberhumer a lossless data compression algorithm
https://en.wikipedia.org/wiki/Lempel-Ziv-Oberhumer], `gzip` footnote:[gzip -
based on the DEFLATE algorithm https://en.wikipedia.org/wiki/Gzip] or `zstd`
footnote:[Zstandard a lossless data compression algorithm
https://en.wikipedia.org/wiki/Zstandard].

Currently, Zstandard (zstd) is the fastest of these three algorithms.
Multi-threading is another advantage of zstd over lzo and gzip. Lzo and gzip
are more widely used and often installed by default.

You can install pigz footnote:[pigz - parallel implementation of gzip
https://zlib.net/pigz/] as a drop-in replacement for gzip to provide better
performance due to multi-threading. For pigz & zstd, the amount of
threads/cores can be adjusted. See the
xref:vzdump_configuration[configuration options] below.

The extension of the backup file name can usually be used to determine which
compression algorithm has been used to create the backup.

|===
|.zst | Zstandard (zstd) compression
|.gz or .tgz | gzip compression
|.lzo | lzo compression
|===

If the backup file name doesn't end with one of the above file extensions, then
it was not compressed by vzdump.

Backup Encryption
-----------------

For Proxmox Backup Server storages, you can optionally set up client-side
encryption of backups, see xref:storage_pbs_encryption[the corresponding section.]

[[vzdump_retention]]
Backup Retention
----------------

With the `prune-backups` option you can specify which backups you want to keep
in a flexible manner. The following retention options are available:

`keep-all <boolean>` ::
Keep all backups. If this is `true`, no other options can be set.

`keep-last <N>` ::
Keep the last `<N>` backups.

`keep-hourly <N>` ::
Keep backups for the last `<N>` hours. If there is more than one
backup for a single hour, only the latest is kept.

`keep-daily <N>` ::
Keep backups for the last `<N>` days. If there is more than one
backup for a single day, only the latest is kept.

`keep-weekly <N>` ::
Keep backups for the last `<N>` weeks. If there is more than one
backup for a single week, only the latest is kept.

NOTE: Weeks start on Monday and end on Sunday. The software uses the
`ISO week date`-system and handles weeks at the end of the year correctly.

`keep-monthly <N>` ::
Keep backups for the last `<N>` months. If there is more than one
backup for a single month, only the latest is kept.

`keep-yearly <N>` ::
Keep backups for the last `<N>` years. If there is more than one
backup for a single year, only the latest is kept.

The retention options are processed in the order given above. Each option
only covers backups within its time period. The next option does not take care
of already covered backups. It will only consider older backups.

Specify the retention options you want to use as a
comma-separated list, for example:

 # vzdump 777 --prune-backups keep-last=3,keep-daily=13,keep-yearly=9

While you can pass `prune-backups` directly to `vzdump`, it is often more
sensible to configure the setting on the storage level, which can be done via
the web interface.

NOTE: The old `maxfiles` option is deprecated and should be replaced either by
`keep-last` or, in case `maxfiles` was `0` for unlimited retention, by
`keep-all`.


Prune Simulator
~~~~~~~~~~~~~~~

You can use the  https://pbs.proxmox.com/docs/prune-simulator[prune simulator
of the Proxmox Backup Server documentation] to explore the effect of different
retention options with various backup schedules.

Retention Settings Example
~~~~~~~~~~~~~~~~~~~~~~~~~~

The backup frequency and retention of old backups may depend on how often data
changes, and how important an older state may be, in a specific work load.
When backups act as a company's document archive, there may also be legal
requirements for how long backups must be kept.

For this example, we assume that you are doing daily backups, have a retention
period of 10 years, and the period between backups stored gradually grows.

`keep-last=3` - even if only daily backups are taken, an admin may want to
  create an extra one just before or after a big upgrade. Setting keep-last
  ensures this.

`keep-hourly` is not set - for daily backups this is not relevant. You cover
  extra manual backups already, with keep-last.

`keep-daily=13` - together with keep-last, which covers at least one
  day, this ensures that you have at least two weeks of backups.

`keep-weekly=8` - ensures that you have at least two full months of
  weekly backups.

`keep-monthly=11` - together with the previous keep settings, this
  ensures that you have at least a year of monthly backups.

`keep-yearly=9` - this is for the long term archive. As you covered the
  current year with the previous options, you would set this to nine for the
  remaining ones, giving you a total of at least 10 years of coverage.

We recommend that you use a higher retention period than is minimally required
by your environment; you can always reduce it if you find it is unnecessarily
high, but you cannot recreate backups once they have been removed.

[[vzdump_protection]]
Backup Protection
-----------------

You can mark a backup as `protected` to prevent its removal. Attempting to
remove a protected backup via {pve}'s UI, CLI or API will fail. However, this
is enforced by {pve} and not the file-system, that means that a manual removal
of a backup file itself is still possible for anyone with write access to the
underlying backup storage.

NOTE: Protected backups are ignored by pruning and do not count towards the
retention settings.

For filesystem-based storages, the protection is implemented via a sentinel file
`<backup-name>.protected`. For Proxmox Backup Server, it is handled on the
server side (available since Proxmox Backup Server version 2.1).

Use the storage option `max-protected-backups` to control how many protected
backups per guest are allowed on the storage. Use `-1` for unlimited. The
default is unlimited for users with `Datastore.Allocate` privilege and `5` for
other users.

[[vzdump_restore]]
Restore
-------

A backup archive can be restored through the {pve} web GUI or through the
following CLI tools:


`pct restore`:: Container restore utility

`qmrestore`:: Virtual Machine restore utility

For details see the corresponding manual pages.

Bandwidth Limit
~~~~~~~~~~~~~~~

Restoring one or more big backups may need a lot of resources, especially
storage bandwidth for both reading from the backup storage and writing to
the target storage. This can negatively affect other virtual guests as access
to storage can get congested.

To avoid this you can set bandwidth limits for a backup job. {pve}
implements two kinds of limits for restoring and archive:

* per-restore limit: denotes the maximal amount of bandwidth for
  reading from a backup archive

* per-storage write limit: denotes the maximal amount of bandwidth used for
  writing to a specific storage

The read limit indirectly affects the write limit, as we cannot write more
than we read. A smaller per-job limit will overwrite a bigger per-storage
limit. A bigger per-job limit will only overwrite the per-storage limit if
you have `Data.Allocate' permissions on the affected storage.

You can use the `--bwlimit <integer>` option from the restore CLI commands
to set up a restore job specific bandwidth limit.  Kibit/s is used as unit
for the limit, this means passing `10240' will limit the read speed of the
backup to 10 MiB/s, ensuring that the rest of the possible storage bandwidth
is available for the already running virtual guests, and thus the backup
does not impact their operations.

NOTE: You can use `0` for the `bwlimit` parameter to disable all limits for
a specific restore job. This can be helpful if you need to restore a very
important virtual guest as fast as possible. (Needs `Data.Allocate'
permissions on storage)

Most times your storage's generally available bandwidth stays the same over
time, thus we implemented the possibility to set a default bandwidth limit
per configured storage, this can be done with:

----
# pvesm set STORAGEID --bwlimit restore=KIBs
----

Live-Restore
~~~~~~~~~~~~

Restoring a large backup can take a long time, in which a guest is still
unavailable. For VM backups stored on a Proxmox Backup Server, this wait
time can be mitigated using the live-restore option.

Enabling live-restore via either the checkbox in the GUI or the `--live-restore`
argument of `qmrestore` causes the VM to start as soon as the restore
begins. Data is copied in the background, prioritizing chunks that the VM is
actively accessing.

Note that this comes with two caveats:

* During live-restore, the VM will operate with limited disk read speeds, as
  data has to be loaded from the backup server (once loaded, it is immediately
  available on the destination storage however, so accessing data twice only
  incurs the penalty the first time). Write speeds are largely unaffected.
* If the live-restore fails for any reason, the VM will be left in an
  undefined state - that is, not all data might have been copied from the
  backup, and it is _most likely_ not possible to keep any data that was written
  during the failed restore operation.

This mode of operation is especially useful for large VMs, where only a small
amount of data is required for initial operation, e.g. web servers - once the OS
and necessary services have been started, the VM is operational, while the
background task continues copying seldom used data.

Single File Restore
~~~~~~~~~~~~~~~~~~~

The 'File Restore' button in the 'Backups' tab of the storage GUI can be used to
open a file browser directly on the data contained in a backup. This feature
is only available for backups on a Proxmox Backup Server.

For containers, the first layer of the file tree shows all included 'pxar'
archives, which can be opened and browsed freely. For VMs, the first layer shows
contained drive images, which can be opened to reveal a list of supported
storage technologies found on the drive. In the most basic case, this will be an
entry called 'part', representing a partition table, which contains entries for
each partition found on the drive. Note that for VMs, not all data might be
accessible (unsupported guest file systems, storage technologies, etc...).

Files and directories can be downloaded using the 'Download' button, the latter
being compressed into a zip archive on the fly.

To enable secure access to VM images, which might contain untrusted data, a
temporary VM (not visible as a guest) is started. This does not mean that data
downloaded from such an archive is inherently safe, but it avoids exposing the
hypervisor system to danger. The VM will stop itself after a timeout. This
entire process happens transparently from a user's point of view.

[[vzdump_configuration]]
Configuration
-------------

Global configuration is stored in `/etc/vzdump.conf`. The file uses a
simple colon separated key/value format. Each line has the following
format:

 OPTION: value

Blank lines in the file are ignored, and lines starting with a `#`
character are treated as comments and are also ignored. Values from
this file are used as default, and can be overwritten on the command
line.

We currently support the following options:

include::vzdump.conf.5-opts.adoc[]


.Example `vzdump.conf` Configuration
----
tmpdir: /mnt/fast_local_disk
storage: my_backup_storage
mode: snapshot
bwlimit: 10000
----

Hook Scripts
------------

You can specify a hook script with option `--script`. This script is
called at various phases of the backup process, with parameters
accordingly set. You can find an example in the documentation
directory (`vzdump-hook-script.pl`).

File Exclusions
---------------

NOTE: this option is only available for container backups.

`vzdump` skips the following files by default (disable with the option
`--stdexcludes 0`)

 /tmp/?*
 /var/tmp/?*
 /var/run/?*pid

You can also manually specify (additional) exclude paths, for example:

 # vzdump 777 --exclude-path /tmp/ --exclude-path '/var/foo*'

excludes the directory `/tmp/` and any file or directory named `/var/foo`,
`/var/foobar`, and so on.

Paths that do not start with a `/` are not anchored to the container's root,
but will match relative to any subdirectory. For example:

 # vzdump 777 --exclude-path bar

excludes any file or directory named `/bar`, `/var/bar`, `/var/foo/bar`, and
so on, but not `/bar2`.

Configuration files are also stored inside the backup archive
(in `./etc/vzdump/`) and will be correctly restored.

Examples
--------

Simply dump guest 777 - no snapshot, just archive the guest private area and
configuration files to the default dump directory (usually
`/var/lib/vz/dump/`).

 # vzdump 777

Use rsync and suspend/resume to create a snapshot (minimal downtime).

 # vzdump 777 --mode suspend

Backup all guest systems and send notification mails to root and admin.

 # vzdump --all --mode suspend --mailto root --mailto admin

Use snapshot mode (no downtime) and non-default dump directory.

 # vzdump 777 --dumpdir /mnt/backup --mode snapshot

Backup more than one guest (selectively)

 # vzdump 101 102 103 --mailto root

Backup all guests excluding 101 and 102

 # vzdump --mode suspend --exclude 101,102

Restore a container to a new CT 600

 # pct restore 600 /mnt/backup/vzdump-lxc-777.tar

Restore a QemuServer VM to VM 601

 # qmrestore /mnt/backup/vzdump-qemu-888.vma 601

Clone an existing container 101 to a new container 300 with a 4GB root
file system, using pipes

 # vzdump 101 --stdout | pct restore --rootfs 4 300 -


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