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Backup and Restore

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 cron entry in /etc/cron.d/vzdump.

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 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).
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. The parameter maxfiles can be used to specify the maximum number of backups to keep.

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 KIBs

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:

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*'

(only excludes tmp directories)

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 -