Here’s a cheat sheet for ZFS snapshots, focusing on essential commands and concepts to help you efficiently work with them.

ZFS Snapshot Basics

  • What is a ZFS Snapshot?
  • A snapshot is a read-only, point-in-time copy of a ZFS file system or volume. It takes almost no space at creation but grows as the data in the file system changes.

1. Creating Snapshots

  • Command: bash zfs snapshot <pool>/<dataset>@<snapshot-name>
  • Example: bash zfs snapshot mypool/mydataset@backup-2024-09-26

2. Listing Snapshots

  • Command: bash zfs list -t snapshot
  • This will show all snapshots with their size and creation date.

3. Renaming Snapshots

  • Command: bash zfs rename <pool>/<dataset>@<old-snapshot-name> <pool>/<dataset>@<new-snapshot-name>
  • Example: bash zfs rename mypool/mydataset@backup-2024-09-26 mypool/mydataset@backup-sept

4. Rolling Back to a Snapshot

  • Command: bash zfs rollback <pool>/<dataset>@<snapshot-name>
  • Rolling back returns the dataset to the state when the snapshot was taken. Note: Any changes made after the snapshot will be lost.
  • Example: bash zfs rollback mypool/mydataset@backup-sept

5. Cloning Snapshots

  • Command: bash zfs clone <pool>/<dataset>@<snapshot-name> <pool>/<new-dataset>
  • Creates a new writeable dataset based on a snapshot.
  • Example: bash zfs clone mypool/mydataset@backup-sept mypool/clone-dataset

6. Deleting Snapshots

  • Command: bash zfs destroy <pool>/<dataset>@<snapshot-name>
  • Example: bash zfs destroy mypool/mydataset@backup-sept
  • Delete multiple snapshots in one go: bash zfs destroy <pool>/<dataset>@<snap1>,<snap2>,<snap3>

7. Incremental Send/Receive with Snapshots

  • Sending a snapshot:
  • Command: bash zfs send <pool>/<dataset>@<snapshot-name> | <destination>

  • Example: bash zfs send mypool/mydataset@backup-sept > /backup/backup-sept.zfs

  • Incremental send between snapshots: bash zfs send -i <snapshot1> <pool>/<dataset>@<snapshot2> | <destination>

  • Example: bash zfs send -i backup-2024-09-20 mypool/mydataset@backup-sept > /backup/diff-backup-sept.zfs

  • Receiving a snapshot:

  • Command: bash zfs receive <pool>/<dataset>
  • Example: bash zfs receive mypool/restore-dataset < /backup/backup-sept.zfs

8. Automatic Snapshot Creation Using cron and zfs-auto-snapshot

  • Install and configure zfs-auto-snapshot:
  • On many systems, you can install zfs-auto-snapshot to automate snapshot creation.
  • Set schedules (e.g., hourly, daily, weekly).

Example usage: bash zfs-auto-snapshot --label=hourly --keep=24 <pool>/<dataset>

9. Showing Differences Between Snapshots

  • Command: bash zfs diff <pool>/<dataset>@<snapshot1> <pool>/<dataset>@<snapshot2>
  • Shows a list of differences between two snapshots.
  • Example: bash zfs diff mypool/mydataset@backup-sept mypool/mydataset@backup-oct

10. Hold/Release Snapshots

  • To prevent a snapshot from being deleted, you can hold it: bash zfs hold <tag> <pool>/<dataset>@<snapshot-name>

  • Example: bash zfs hold keep mypool/mydataset@backup-sept

  • To release it: bash zfs release <tag> <pool>/<dataset>@<snapshot-name>

  • Example: bash zfs release keep mypool/mydataset@backup-sept

11. ZFS Snapshot Retention Policies (Manual Cleanup)

  • It’s good practice to periodically delete old snapshots, which can be done manually using zfs destroy or automated with a custom script or tools like zfs-auto-snapshot.

12. Snapshot Space Usage

  • Check how much space snapshots are using: bash zfs list -t snapshot

13. Exporting a Pool with Snapshots

  • Command: bash zpool export <pool-name>

Useful Commands Summary:

  • Create: zfs snapshot <pool>/<dataset>@<name>
  • List: zfs list -t snapshot
  • Rollback: zfs rollback <pool>/<dataset>@<name>
  • Send: zfs send <pool>/<dataset>@<name> | <destination>
  • Receive: zfs receive <pool>/<dataset>
  • Clone: zfs clone <pool>/<dataset>@<name> <pool>/<clone-name>
  • Delete: zfs destroy <pool>/<dataset>@<name>
  • Hold: zfs hold <tag> <pool>/<dataset>@<name>
  • Release: zfs release <tag> <pool>/<dataset>@<name>

This cheat sheet should help streamline your ZFS snapshot operations! Let me know if you need more details on any of the commands or features.