ZnapZend is a ZFS centric backup tool to create snapshots and send them to backup locations. It relies on the ZFS tools snapshot, send and receive to do its work. It has the built-in ability to manage both local snapshots as well as remote copies by thinning them out as time progresses.
The ZnapZend configuration is stored as properties in the ZFS filesystem itself.
Note that while recursive configurations are well supported to set up backup and retention policies for a whole dataset subtree under the dataset to which you have applied explicit configuration, at this time pruning of such trees ("I want every dataset under var except var/tmp") is not supported. You probably do not want to enable ZnapZend against the root datasets of your pools due to that, but would have to be more fine-grained in your setup. This is consistent with (and due to) usage of recursive ZFS snapshots, where the command is targeted at one dataset and impacts it and all its children, allowing to get a consistent point-in-time set of snapshots across multiple datasets.
If your distribution does not provide a packaged version of znapzend, or if you want to get a custom-made copy of znapzend, you will need a compiler and stuff to build some of the prerequisite perl modules into binary libraries for the target OS and architecture. For run-time you will need just perl.
On RedHat you get the necessaries with:
yum install perl-core
On Ubuntu / Debian with:
apt-get install perl unzip
On Solaris you may need the C compiler from Solaris Studio and gnu-make since the installed perl version is probably very old.
On OmniOS/SmartOS you will need perl and gnu-make.
On macOS, if you have not already installed the Xcode command line tools, you can get them from the command line (Terminal app) with:
xcode-select --install (or just install the full Xcode app from the Apple app store).
With that in place you can now utter:
wget https://github.com/oetiker/znapzend/releases/download/v0.19.2/znapzend-0.19.2.tar.gz tar zxvf znapzend-0.19.2.tar.gz cd znapzend-0.19.2 ./configure --prefix=/opt/znapzend-0.19.2
If configure finds anything noteworthy, it will tell you about it. If any perl modules are found to be missing, they get installed locally into the znapzend installation. Your perl installation will not get modified!
make make install
Optionally (but recommended) put symbolic links to the installed binaries in the system PATH.
for x in /opt/znapzend-0.19.2/bin/*; do ln -s $x /usr/local/bin; done
Debian control files, guide on using them and experimental debian packages can be found at https://github.com/Gregy/znapzend-debian
An RPM spec file can be found at https://github.com/asciiphil/znapzend-spec
dnf copr enable spike/znapzend dnf install znapzend
For Gentoo there's an ebuild in the gerczei overlay.
Use the znapzendzetup program to define your backup settings. They will be stored directly in dataset properties, and will cover both local snapshot schedule and any number of destinations to send snapshots to (as well as potentially different retention policies on those destinations). You can enable recursive configuration, so the settings would apply to all datasets under the one you configured explicitly.
znapzendzetup create --recursive\ --pre-snap-command="/bin/sh /usr/local/bin/lock_flush_db.sh" \ --post-snap-command="/bin/sh /usr/local/bin/unlock_db.sh" \ SRC '7d=>1h,30d=>4h,90d=>1d' tank/home \ DST:a '7d=>1h,30d=>4h,90d=>1d,1y=>1w,10y=>1month' root@bserv:backup/home
See the znapzendzetup manual for the full description of the configuration options.
For remote backup, znapzend uses ssh. Make sure to configure password-free login (authorized keys) for ssh to the backup target host with an account sufficiently privileged to manage its ZFS datasets under a chosen destination root.
For local or remote backup, znapzend can use mbuffer to level out the bursty nature of ZFS send and ZFS receive features, so it is quite beneficial even for local backups into another pool (e.g. on removable media or a NAS volume). It is also configured among the options set by znapzendzetup per dataset. Note that in order to use larger (multi-gigabyte) buffers you should point your configuration to a 64-bit binary of the mbuffer program. Sizing the buffer is a practical art, depending on the size and amount of your datasets and the I/O speeds of the storage and networking involved. As a rule of thumb, let it absorb at least a minute of I/O, so while one side of the ZFS dialog is deeply thinking, another can do its work.
The znapzend daemon is responsible for doing the actual backups.
To see if your configuration is any good, run znapzend in noaction mode first.
znapzend --noaction --debug
If you don't want to wait for the scheduler to actually schedule work, you can also force immediate action by calling
znapzend --noaction --debug --runonce=<src_dataset>
then when you are happy with what you got, start it in daemon mode.
Best practice is to integrate znapzend into your system startup sequence, but you can also run it by hand. See the init/README.md for some inspiration.
Running by an unprivileged user
In order to allow a non-privileged user to use it, the following permissions are required on the ZFS filesystems:
Sending end: destroy,hold,mount,send,snapshot,userprop Receiving end: create,mount,receive,userprop
Running in Container
znapzend is also available as docker container image. It needs to be a privileged container depending on permissions.
docker run -d --name znapzend --device /dev/zfs --privileged oetiker/znapzend:master
To configure znapzend, run in interactive mode:
docker exec -it znapzend /bin/sh $ znapzendzetup create ... # After exiting, restart znapzend container or send the HUP signal to reload config
By default, znapzend in container runs with
--logto /dev/stdout. If you wish to add different arguments,
overwrite them at the end of the command:
docker run --name znapzend --device /dev/zfs --privileged oetiker/znapzend:master znapzend --logto /dev/stdout --runonce --debug
Be sure not to daemonize znapzend in the container, as that exits the container immediately.
By default a znapzend daemon would log its progress and any problems to local syslog as a daemon facility, so if the service misbehaves - that is the first place to look. Alternately, you can set up the service manifest to start the daemon with other logging configuration (e.g. to a file or to stderr) and perhaps with debug level enabled.
In case you tinkered with ZFS attributes that store ZnapZend retention
policies, or potentially if you have a severe version mismatch of ZnapZend
(e.g. update from a PoC or very old version),
znapzendzetup list is
quite useful to non-intrusively discover whatever your current version can
consider to be discrepancies in your active configuration.
If you want to know how much space your backups are using, try the znapzendztatz utility.
Support and Contributions
If you find a problem with znapzend, please open an Issue on GitHub.
And if you have a contribution, please send a pull request.
Dominik Hassler & Tobi Oetiker 2020-03-23