Backup Strategies

ZFS provides flexible and efficient methods for creating backups, primarily using snapshots and replication. Snapshots are used to capture point-in-time versions of datasets, which can then be stored locally, sent to remote systems, or transferred to offsite locations for backup and disaster recovery.

Using Snapshots for Backups

A snapshot in ZFS is a read-only copy of a dataset at a specific moment in time. Snapshots are efficient because they initially consume no additional space, only recording changes made after the snapshot is taken. This makes them an ideal tool for regular backups.

To create a snapshot for backup purposes, use the following command:

$ sudo zfs snapshot mypool/mydataset@snapshotname

This snapshot can be used for both local backups and as the source for replication to a remote system. Snapshots can be created manually or automated using tools like cron jobs or other scheduling systems.

Automating snapshot creation is a key strategy for maintaining regular backups. For example, to create a daily snapshot of a dataset, a cron job can be set up as follows:

0 2 * * * sudo zfs snapshot mypool/mydataset@$(date +\%Y-%m-%d)

This command creates a snapshot every day at 2 AM, with the date appended to the snapshot name.

Snapshots can be retained for different periods, such as hourly, daily, weekly, or monthly, depending on the backup retention policy. For example, the zfs-auto-snapshot tool can automate snapshot creation and manage retention policies.

To list all available snapshots:

$ sudo zfs list -t snapshot

Snapshots provide several advantages for backups:

• Efficient Storage: Snapshots only consume space as changes are made after the snapshot, so they are space-efficient.
• Quick Recovery: Snapshots allow for fast recovery from accidental deletions or data corruption by rolling back the dataset to a previous state.

Offsite and Remote Backups

For additional data security, especially in disaster recovery scenarios, offsite or remote backups are essential. ZFS supports efficient remote backups through replication, allowing snapshots to be transferred to another system, either locally or remotely.

Remote Backups with ZFS Replication

Remote backups can be accomplished using ZFS replication. Replication enables the sending of snapshots to a remote system, ensuring that a full or incremental copy of the dataset is available for recovery in the event of local system failure.

To replicate a snapshot to a remote system for backup:

1. First, create a snapshot:

$ sudo zfs snapshot mypool/mydataset@snapshotname

2. Then, send the snapshot to the remote system:

$ sudo zfs send mypool/mydataset@snapshotname | ssh remotesystem sudo zfs receive remotepool/mydataset

For incremental backups, which transfer only the changes made since the last snapshot:

$ sudo zfs send -i mypool/mydataset@previous_snapshot mypool/mydataset@latest_snapshot | ssh remotesystem sudo zfs receive remotepool/mydataset

This method efficiently backs up only the differences between the previous and current snapshots, minimizing bandwidth usage and reducing backup time.

Offsite Backups

Offsite backups are critical for disaster recovery and protection against local system failures or catastrophic events like fires or floods. There are several strategies for implementing offsite backups in ZFS:

1. Physical Offsite Backups: Datasets can be backed up to external storage devices (such as USB drives or removable media) and stored at an offsite location. The ZFS send command can be used to transfer snapshots to these external drives:

$ sudo zfs send mypool/mydataset@snapshotname > /media/usbdrive/backupfile

This file can then be physically moved to a secure offsite location.

2. Cloud and Remote Server Backups: ZFS snapshots can be sent to cloud servers or remote data centers using replication over SSH. This is similar to the remote backup strategy but involves sending the data to a cloud storage provider or secondary data center instead of a local system.

For example, to send backups to a cloud server:

$ sudo zfs send mypool/mydataset@snapshotname | ssh cloudserver sudo zfs receive cloudpool/mydataset

This command replicates the snapshot to the cloud storage system, ensuring that a remote backup is always available.

Backup Retention Policies

When implementing backup strategies, it is important to define a retention policy that determines how long snapshots and backups are retained. Snapshots can accumulate over time, consuming space, so it is necessary to periodically delete older snapshots:

$ sudo zfs destroy mypool/mydataset@old_snapshot

Automated tools like zfs-auto-snapshot can be used to manage snapshot retention policies, ensuring that recent snapshots are kept while older ones are removed based on predefined rules (e.g., keep daily snapshots for one month, weekly snapshots for six months, etc.).