ZFS send end receive for backups ================================ ZFS is a wonderful file system ------------------------------ ZFS is a wonderful file system with many advantages. People write entire books about ZFS, this post only scratches the surface. FreeBSD has long supported ZFS, including the usage of ZFS on the root file system, paving the way for so-called boot environments. ZFS also runs on Linux and offers some of its advantages there too. ZFS snapshots ------------- A great feature of ZFS is the capability of taking snapshots. A snapshot is like a photo of your file system, it freezes a moment in time. Because ZFS is a so called `Copy on Write' file system (CoW), the creation of a snapshot is instantaneous. ZFS snapshots use space on the same storage pool as the file system from which they are created. A fresh snapshot consumes nearly no space, changes of the live file system will grow the size of the snapshot. Rolling back and cloning of snapshots ------------------------------------- A roll-back of a ZFS snapshot restores the file system to the state at the moment the snapshot was created. It discards all the changes made since the specific snapshot. Subsequent snapshots allow you to choose the point in time to go back to. Some people for example let their system make a snapshot of their home directory every ten minutes. Another example is making snapshots just before changes like installing or updating packages. A clone of a ZFS snapshot replicates the snapshot on a different location within the ZFS file system. The creation of a clone is instantaneous. Snapshots and clones add a whole new dimension to the deployment of containers like jails and virtual machines because of this. ZFS send and receive -------------------- ZFS send and receive moves snapshots efficiently. ZFS send and receive can be done within the same system, but is most used to move snapshots to other systems. ZFS send can dispatch incremental data. In this case, the difference between two subsequent snapshots is transported to the receiving system. This requires the snapshots on the sending and the receiving machines to be in sync. The first time sending a snapshot takes considerate time. It is best to do this from within tmux. Sending subsequent incremental snapshots take much less time. Daily backup using ZFS send and receive --------------------------------------- The example script below creates a snapshot and leverages the use of sending incremental data to efficiently send it to another machine. This assumes that the first snapshot is send normally to the receiving machine. In this example: * both systems run ZFS * the dataset to snapshot is called `myset' * the receiving system is called `receiver', this can be a hostname or an ip-address * zstdmt is used to compress the data before sending * zstd is used to decompress the data on the receiving system * the user on the sending system has password-less ssh access to the receiving system * the user on the sending and the receiving system has the proper permissions for this action #!/bin/sh mydate=$(date "+%Y-%m-%d-%H:%M") /sbin/zfs snapshot zroot/myset@$mydate previous=$(/sbin/zfs list -t snapshot | grep myset | sort -rn | head -n 2 | tail -n 1 | cut -d' ' -f 1) /sbin/zfs send -i $previous zroot/myset@$mydate | zstdmt | ssh receiver "zstd -d | zfs receive zroot/backups/myset@$mydate" This script can be run from cron, for example every hour or every night. Result ------ The data now lives on two machines. `zfs list -t snapshot' on both the sending and the receiving system lists the subsequent snapshots of `myset'. When on the receiving system a mount point is set for zroot/backups/myset the data can be access there normally. However, be careful not to change the data on the receiving machine, because this results the data between the two systems being out of sync. Working with non-root users --------------------------- Some advantages of the ability to run the preceding script as a non-root user on both the sending and the receiving system are: * the user can choose any convenient moment to perform the action * no need for root ssh access on the receiving system Delegate permissions for a specific dataset with `zfs allow' at a fine grained level like create, destroy, mount, snapshot, and so on. To allow a user to create a snapshot of a specific dataset and to send that snapshot, use the following command: zfs allow hold,mount,send,snapshot zroot/myset And on the receiving system: zfs allow create,mount,receive zroot/backups Permissions can be retracted with `zfs unallow'. To list the current permissions use `zfs allow ' without any options, like: zfs allow zroot/myset Clean up -------- It's not necessary to keep old snapshots. Delete old snapshots on a regular basis to avoid wasting storage space. Last edited: $Date: 2024/01/01 16:30:23 $