There are several ways to provide consistency (option mode
),
depending on the guest type.
Backup modes for VMs:
stop
mode
suspend
mode
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
agent: 1
) and running, it calls
guest-fsfreeze-freeze
and guest-fsfreeze-thaw
to improve
consistency.
A technical overview of the Proxmox VE live backup for QemuServer can be found online here.
Proxmox VE 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
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
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).
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 Proxmox VE storage library.