Why does my QNAP NAS use swap space even when there is free memory available?
Applicable Products
NAS (QTS / QuTS Hero)
Scenario
I observe that the swap space is used even though half of the system memory is still free. Why?
Solution
This behavior is normal and does not necessarily indicate a problem with your NAS. Modern operating systems (including QTS and QuTS hero, which are based on Linux) may allocate swap space even when physical memory (RAM) is not fully utilized.
Reasons include:
Memory Optimization by Kernel
The Linux kernel may move infrequently used data from RAM to swap, keeping more RAM available for file system cache and frequently accessed applications.
This improves overall responsiveness, especially for services that require fast access to cached data.
System Stability
Using swap as a buffer prevents applications from running out of memory when workload spikes occur.
Even if there is “free” RAM, the system may still choose to swap out idle memory pages proactively.
Container and Virtualization Workloads
When running Virtualization Station, Container Station, or apps with large memory footprints, the system may swap to maintain memory isolation between applications.
- Background Services
- Some services (e.g., indexing, multimedia applications, backup tasks) may trigger swap usage temporarily, even if memory usage appears moderate.
Swap usage on QNAP NAS is expected behavior and part of how the system manages memory efficiently. Small amounts of swap usage are normal and not a cause for concern. If performance issues occur under heavy workloads, upgrading RAM is the best long-term solution.
