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ZFS tools

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The ZFS backup tools will help you graft an entire ZFS pool as a filesystem into a backup machine, without having to screw around snapshot names or complicated shell commands or crontabs.

The utilities let you do this:

  1. zfs-shell:
    a shell that allows remote ZFS administration and nothing more

  2. zsnap:
    a command that snapshots a dataset or pool, then deletes old snapshots

  3. zreplicate
    a command that replicates an entire dataset tree using ZFS replication streams. Best used in combination with zsnap as in:

    • zsnap on the local machine
    • zreplicate from the local machine to the destination machine

    Obsolete snapshots deleted by zsnap will be automatically purged on the destination machine by zreplicate, as a side effect of using replication streams. To inhibit this, use the --no-replication-stream option.

    Run zreplicate --help for a compendium of options you may use.

  4. zbackup: a command to snapshot and replicate filesystems according to their user properties. This uses zsnap and zreplicate to do the work, which is all driven by properties. For details, see this further description of zbackup.

  5. zflock: a command to lock a filesystem against replication by zbackup. For details, see this further description of zbackup.

The repository, bug tracker and Web site for this tool is at http://github.com/Rudd-O/zfs-tools. Comments to me through [email protected].

Setting up

Setup is rather complicated. It assumes that you already have ZFS running and vaults on both the machine you're going to back up and the machine that will be receiving the backup.

On the machine to back up

  • Install the zfs-shell command
    cp zfs-shell /usr/local/sbin
    chmod 755 /usr/local/sbin/zfs-shell
    chown root.root /usr/local/sbin/zfs-shell

  • Create a user with a home directory and shell zfs-shell
    useradd -rUm -b /var/lib -s /usr/local/sbin/zfs-shell zfs

  • Let sudo know that the new user can run the zfs command
    zfs ALL = NOPASSWD: /usr/local/sbin/zfs
    (ensure you remove the requiretty default on /etc/sudoers) (check sudoers.zfs-tools in contrib/ for an example)

  • Set up a cron job to run zsnap as frequently as you want to, snapshotting the dataset you intend to replicate.

On the backup machine

  • Set up public key authentication for SSH so the backup machine may log as the user zfs (as laid out above) in the machine to be backed up.

  • Create a dataset to receive the backup stream.

  • Set up a cron job to fetch the dataset snapshotted by zsnap from the remote machine into the newly created dataset. You will use zreplicate for that (see below for examples).

  • After the first replication, you may want to set the mountpoint attributes on the received datasets so they do not automount on the backup machine.

Test

If all went well, you should be able to do this without issue:

(on the machine to back up)

[root@peter]
zsnap senderpool

(on the machine to receive)

[root@paul]
zfs create receiverpool/senderpool # <--- run this ONLY ONCE
zreplicate -o zfs@paul:senderpool receiverpool/senderpool
# this should send the entire senderpool with all snapshots
# over from peter to paul, placing it in receiverpool/senderpool

(on the machine to back up)

[root@peter]
zsnap senderpool

(on the machine to receive)

[root@paul]
zreplicate -o zfs@paul:senderpool receiverpool/senderpool
# this should send an incremental stream of senderpool
# into receiverpool/senderpool

And that's it, really.