Fact Check: Are ZFS snapshots incremental?

Are ZFS Snapshots Incremental?

The claim in question is whether ZFS (Zettabyte File System) snapshots are incremental. This inquiry revolves around the functionality of ZFS snapshots and their use in data backup and recovery processes.

What We Know

1. ZFS Snapshots: ZFS allows users to create snapshots of file systems, which are read-only copies of the file system at a specific point in time. These snapshots can be used for backup and recovery purposes. According to the ZFS Administration Guide, snapshots are efficient and can be created quickly without consuming additional space initially, as they only record changes made after the snapshot was taken 3.

2. Incremental Backups: The concept of incremental backups involves saving only the changes made since the last backup. ZFS supports this through the zfs send -I command, which allows users to send incremental data between snapshots. This means that if you have a snapshot from a previous date, you can create a new snapshot and use the incremental send feature to back up only the changes 49.

3. Interdependence of Snapshots: Incremental snapshots in ZFS are interdependent. If an older snapshot that is part of an incremental backup chain is deleted, it can render subsequent snapshots unusable, as they rely on the existence of earlier snapshots 7. This highlights the importance of managing snapshots carefully to maintain data integrity.

4. Efficiency of Incremental Backups: The use of incremental backups in ZFS is noted for its efficiency, particularly in reducing the amount of data transferred during backup operations. This is especially useful in environments where bandwidth is limited or where storage resources need to be optimized 10.

Analysis

Source Evaluation

• Technical Documentation: Sources such as the ZFS Administration Guide 3 and Oracle Help Center 9 provide authoritative information on ZFS functionality. These documents are produced by organizations with expertise in storage systems, lending them credibility. However, they may present information with a bias towards promoting their own technologies.

• Community Insights: User-generated content from forums like ServerFault 2 and FreeBSD forums 7 can provide practical insights and real-world applications of ZFS. However, these sources may contain anecdotal evidence and personal opinions, which should be weighed against more formal documentation.

• Blogs and Guides: Articles from independent blogs, such as the one on xai.sh 1 and Grendelman's site 5, offer practical examples and use cases. While these can be informative, the credibility of these sources can vary based on the author's expertise and potential biases.

Methodological Considerations

The claim that ZFS snapshots are incremental is supported by multiple sources that describe the functionality of the zfs send -I command. However, the interpretation of what constitutes "incremental" may vary. For instance, while ZFS allows for incremental data transfers, the management of snapshots and their interdependencies adds complexity that users must navigate.

Conflicts of Interest

Some sources, particularly those from Oracle, may have a vested interest in promoting ZFS as a superior file system. This could influence the presentation of information, emphasizing strengths while downplaying limitations. Independent blogs may also have biases based on the author's experiences or preferences for specific technologies.

Conclusion

Verdict: True

The claim that ZFS snapshots are incremental is substantiated by multiple credible sources, including technical documentation and user experiences. The zfs send -I command enables users to perform incremental backups by transferring only the changes made since the last snapshot. This functionality is particularly advantageous in optimizing storage and bandwidth during backup operations.

However, it is important to note that the interdependence of snapshots introduces complexity in managing them. Deleting older snapshots can compromise the integrity of subsequent incremental backups. Therefore, while the functionality exists, users must exercise caution in managing their snapshots to ensure data integrity.

Additionally, the evidence primarily comes from technical documentation and community discussions, which may carry inherent biases. Readers should critically evaluate the information and consider their specific use cases when implementing ZFS snapshots for incremental backups.

Sources

1. Incremental backups with zfs send/recv - ./xai.sh. Available at: https://xai.sh/2018/08/27/zfs-incremental-backups.html
2. How to perform incremental / continuous backups of zfs pool? - ServerFault. Available at: https://serverfault.com/questions/842531/how-to-perform-incremental-continuous-backups-of-zfs-pool
3. Working With ZFS Snapshots and Clones - ZFS Administration Guide - illumos. Available at: https://www.illumos.org/books/zfs-admin/snapshots.html
4. Sending and Receiving ZFS Data - Oracle Documentation. Available at: https://docs.oracle.com/cd/E19253-01/819-5461/gbchx/index.html
5. Fast & frequent incremental ZFS backups with zrep - Grendelman. Available at: https://www.grendelman.net/wp/fast-frequent-incremental-zfs-backups-with-zrep/
6. NDMP Incremental Backups - Oracle Help Center. Available at: https://docs.oracle.com/en/storage/zfs-storage/zfs-appliance/os8-8-x/admin-guide/ndmp-incremental-backups.html
7. Incremental snapshot confusion - ZFS - FreeBSD Forums. Available at: https://forums.freebsd.org/threads/incremental-snapshot-confusion.74297/
8. Oracle Solaris ZFS Administration Guide. Available at: https://docs.oracle.com/cd/E19253-01/819-5461/gfwqb/index.html
9. Sending a ZFS Snapshot - Oracle Help Center. Available at: https://docs.oracle.com/en/operating-systems/solaris/oracle-solaris/11.4/manage-zfs/sending-a-zfs-snapshot.html
10. Replication | ZFS Handbook. Available at: https://www.zfshandbook.com/docs/backup-and-recovery/replication/