# zfs-snapshot-backup

** Automatically create (incremental) backups of zfs snapshots on a file server. **


This is currently tailored only to our setup of a FreeNAS in combination with
our virtual server and storage provided by the Rechenzentrum.

The script will create backups of ZFS snapshots for elab journals. The name of
the ZFS dataset (from wich the snapshots are created) must start with `elabfs-`
followed by the elab member name, e.g. `LukasMetzler`

The snapshots should be made with the `periodic snapshot task` provided by the
FreeNAS system. Snapshots should be kept on the NAS for a couple of days
(currently one week) to allow transfer errors not to interfere with the backup
process.

The backup process should be run after a snapshot is taken. Proposed is to take
a daily snapshot at night (currently between 2am and 3am) and start the backup
process later via cron (currently set to 4am).

The documentation in our wiki can be found at:
https://wiki.cpi.imtek.uni-freiburg.de/CPIvServerDocumentation/ElabOnZfs


## restoring backups ##

1. copy a snapshot backup to the NAS

    ```
    cd /mnt/Datenspeicher/snap-backup-dataset/temporary-backups/
    scp -i ../backup_key zfs_snap_backup@etha.cpi.imtek.uni-freiburg.de:~/zfs-backups/<member-name>/<backup-file> tmp-backup-file.gz
    ```

2. unzip the backup file and restore it into a dataset

    ```
    gunzip -c tmp-backup-file.gz | zfs receive -F Datenspeicher/test-backup
    ```

3. remove the (local) backup file

    ```
    rm tmp-backup-file.gz
    ```


## notes on implementation ##

At first I tried to implement the complete process in one python file, but this
lead to an unforseen (and very strange) error:

The created gzip file was not completely written before copying it to the remote
server. Even closing the file descriptor manually or waiting for a very long
time would not solve the problem. The gzip was only completed if the python
process was stopped.

Therefore creating the backups and copying them to the remote server is now a
two step process, combined in the `run_snapshot_backups.sh` shell script.

I have the idea, that it has todo with the copy on write feature of zfs, but
I'm not sure about it.