How QuTS hero NAS reacts to memory exhaustion and what to do about it
Last modified date:
2025-06-11
Applicable Products
QuTS hero
Symptom
Symptom ZFS under QuTS hero requires a large amount of memory to function efficiently. If system memory is insufficient, the following symptoms may occur:
- Severe Performance Degradation QuTS hero uses ARC (Adaptive Replacement Cache) to improve read performance and reduce disk I/O. A lack of memory reduces ARC effectiveness, resulting in more direct disk access and noticeable performance drops.
- Process Freezes or D-State Hang During memory pressure, processes interacting with ZFS metadata may become stuck in uninterruptible I/O wait (D-state), especially during high write activity, scrubbing, or resilvering.
- System Out of Memory (OOM) To free up memory, the system kernel may forcibly terminate processes (including non-ZFS services). This not only disrupts running services but may also impact overall system stability.
Solution
Increase the system memory. ZFS in QuTS hero is optimized for high-memory environments. Adding RAM improves ARC cache hit rates, prevents process hangs and OOM events, and helps maintain both service and system stability. Refer to your NAS model’s specifications for supported RAM and follow official QNAP procedures for memory upgrades.
