Why maps are disappearing after crashes
Over the past year, players have occasionally reported that their maps suddenly reverted to blank after a server crash. What at first seemed like an isolated issue turned out to be a fundamental limitation in how Minecraft and our server platform handle map saving.
Let’s take a closer look.
Main takeaways:
- Map data is stored in memory and only flushed to disk during a proper shutdown.
- With Folia's multithreading, this becomes potentially riskier if the server crashes.
- As uptime increases, more map data is at risk if the server goes down unexpectedly.
- We're implementing changes to prevent permanent loss, but the solution isn't trivial.
Why it happens
Since transitioning to Folia, the server has been more stable and can run much longer without restarting. That’s great for performance and player experience, but it means more data lives temporarily in memory.
When a player creates a map, Minecraft stores the data in RAM. The map's .dat file only gets written during a clean shutdown. If the server crashes, that in-memory map data is lost.
On older versions or with frequent restarts, this wasn’t as noticeable. Now that EarthMC can go a full week without rebooting, a crash at the wrong time can wipe out days' worth of maps.
Why we can't just restore the files
We’ve tried creating tools that intercept map data from packets and save it manually. But even with complete visuals (like the pixels and map ID), Minecraft expects:
- Properly aligned metadata like
xCenter,zCenter, andscale - All the color information (how the map actually displays)
- Internal consistency with Minecraft’s native NBT format
If any of those are wrong or missing, Minecraft rejects the map entirely. Not to mention this would not account for maps updated after creation, or a variety of other factors.
While it is possible in theory to reconstruct some .dat files, many get flagged as corrupt, even when they look fine from the outside.
Why this is hard to fix (and what it means)
The problem lies in how Minecraft handles maps. Unlike players, or plugin data from Towny such as towns and nations, maps are stored in a special binary format and don’t autosave in real-time.
Even with advanced plugin tooling, we can’t safely intercept the full internal map structure while the server is live. That would require:
- A native server patch, not a plugin
- Possible deep integration with Minecraft’s internals
- Unsafe or unsupported APIs that risk corrupting other data
This puts the solution outside the scope of typical plugin development. An external backup system that automatically backs up these maps in the event of a crash, would be the specialized solution to work towards.
What we’re doing about it
- Working with staff to help recover lost maps from before the crash: Staff may be able to manually roll back maps at platforms, depending on the time of the map being made and other factors. However, this process is time-consuming and situational, especially without guaranteed recovery of recent changes. If you lost an important map, it's worth making a ticket. Even if we can’t recover everything, staff will do their best to assist.
- Introducing more frequent server restarts: In order to limit how much data lives only in memory.
- Planning for a longer-term solution: An autonomous solution involving backing up maps consistently in the event of a loss of data.
Instead of letting the server run for a full week, we’ll restart more frequently to ensure map saves flush to disk. If the server crashes, only that brief uptime of maps are lost, not the entire week’s.
If your map disappeared
If you made a map after April 6, it may be recoverable. Please open a ticket and provide the map ID and the approximate time and coordinate location it was created in.
Final thoughts
Map saving isn’t broken, but it is fragile. This is a conscious dilemma which requires us to think about what data is actually safe.
Thanks for your patience while we investigate, and apologies for the inconvenience incurred. It is understandably frustrating to lose weeks of work, gameplay progress, and most notably your time. While we previously believed this issue to be rare and manageable, it’s now clear that its impact has been far more severe, frequent, and damaging than we had acknowledged. We’ll keep you updated on future improvements and solutions being pursued.