Rolling Back the Clock: How ZFS Snapshots Work on Your InterServer VPS

So, you’ve just signed up for an InterServer VPS, or maybe you’re considering it. One of the most powerful tools at your disposal is the ZFS file system. It comes with a “safety net” feature called snapshots. But before you hit that “rollback” button, it’s important to understand exactly what happens to your data—and your timeline.

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Quick Start: What is a ZFS Snapshot?

Think of a ZFS snapshot as a read-only “photograph” of your entire file system at a specific moment in time. It doesn’t copy all your files to a new location; instead, it records the state of your data. Because of how ZFS handles data, these snapshots are nearly instantaneous and don’t take up much space initially.

On an InterServer VPS, the system generally attempts to keep three snapshots available (resource permitting):

• First Snapshot: 24 hours old
• Second Snapshot: 48 hours old
• Third Snapshot: 72 hours old

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The “Not a Backup” Warning

It is tempting to think of snapshots as a complete backup, but they aren’t. Here is why:

• Storage Dependency: Snapshots live on the same physical disks as your live data. If the hardware fails, you lose both the live data and the snapshots.
• Local Only: A real backup should be stored in a separate physical location.

Pro Tip: Always maintain an external backup of your critical databases and files. Snapshots are for quick “oops” moments; backups are for disasters.

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The Rollback: What Happens to Your Timeline?

When you “roll back,” you are telling the server to return to the exact state it was in when a specific snapshot was taken. However, ZFS follows a linear timeline. This means that rolling back to an older point in time effectively “erases” the history that happened after it.

Scenario 1: Restoring the Third (72-hour) Snapshot

If you restore the oldest snapshot (the Third), nothing is deleted from your snapshot list. The Second (48hr) and First (24hr) snapshots still exist in the future relative to that point. You are simply moving the “Live” state of the server back to the 72-hour mark.

Scenario 2: Restoring the Second (48-hour) Snapshot

If you restore the Second snapshot:

• The Third (72hr) snapshot is removed.
• The First (24hr) snapshot remains.

Scenario 3: Restoring the First (24-hour) Snapshot

If you restore the newest snapshot (the First):

• Both the Second and Third snapshots are removed.
• Your system becomes the First snapshot.

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Why do some snapshots disappear after a rollback?

This is the most common question users have. ZFS snapshots are incremental. Each snapshot relies on the one taken before it to track changes.

When you roll back to the most recent snapshot (the 24-hour one), you are essentially telling the system, “Discard everything that happened before this point and make this the new starting line.” Because the 48-hour and 72-hour snapshots represent a history that is now behind your current restored state in the file system’s logic, ZFS clears them out to maintain a clean, linear path of data.

The Golden Rule: Always start your restoration attempts with the first (newest) snapshot if you aren’t sure which one you need. If you start with the oldest one, you loose the ability to try the newer snapshots!

Questions? Please reach out to support via https://my.interserver.net