ProxmoxVE - TrueNAS VM - Disable Memory Ballooning

ProxmoxVE - TrueNAS VM - Disable Memory Ballooning#

ProxmoxVE's memory ballooning feature allows a virtual machine's operating system to dynamically adjust its reported memory usage. This enables the hypervisor (ProxmoxVE) to reclaim memory from the VM if it's not actively being used by the guest OS, and allocate it to other VMs or the host.

However, for TrueNAS virtual machines, memory ballooning should be disabled.

TrueNAS, and particularly its underlying ZFS filesystem, relies heavily and directly on RAM for its Adaptive Replacement Cache (ARC). The ARC is crucial for ZFS pool read performance, and ZFS is designed to manage its own memory usage for the ARC very carefully.

Why Memory Ballooning is Problematic for TrueNAS/ZFS:

• ARC Instability & Performance Degradation: If ProxmoxVE reclaims memory via ballooning that ZFS believes is available for its ARC, it can force the ARC to shrink inefficiently or unpredictably. This starves ZFS of necessary cache, leading to significantly degraded pool performance, especially for reads.
• ZFS Memory Management Conflict: ZFS expects stable and exclusive control over its allocated RAM. Ballooning introduces an external mechanism that can interfere with ZFS's internal memory management algorithms, which are highly optimized.
• Potential for System Instability: While less common, severe memory contention or unexpected changes in available RAM due to ballooning could, in extreme cases, impact the overall stability of the TrueNAS system or the ZFS pool, as ZFS services might struggle if memory is suddenly reclaimed.

Recommendation:

When configuring a TrueNAS VM in ProxmoxVE:

1. Assign a static amount of RAM to the TrueNAS VM. Ensure this meets TrueNAS's minimum requirements (typically 8GB, with 1GB per TB of storage often cited as a good rule of thumb for optimal performance, though this varies by workload).
2. Disable memory ballooning explicitly. In ProxmoxVE's VM settings for the TrueNAS VM, under "Hardware," find the "Memory" section and ensure the "Ballooning Device" checkbox is unchecked.

This ensures that TrueNAS has dedicated access to all the RAM you've allocated to it, allowing ZFS to manage its ARC effectively for optimal performance and stability.

Related Internal Notes#

• ZFS - Adaptive Replacement Cache (ARC) Explained
• TrueNAS - VM Sizing and Configuration Best Practices
• ProxmoxVE - VM Performance Tuning

Further Reading & Resources#

• TrueNAS Community Forums & Documentation: Discussions often highlight the importance of static memory for ZFS. While direct links change, searching their forums for "ZFS ARC memory ballooning" or "TrueNAS VM memory" will yield many relevant discussions.
• A general starting point for TrueNAS hardware guidance: TrueNAS CORE Hardware Guide (servethehome.com) (While not specifically about ballooning, it emphasizes ZFS's RAM needs).
• Proxmox VE Documentation/Wiki: Check for best practices when virtualizing storage-heavy systems.
• General ZFS Memory Management Articles:
• An older but still conceptually relevant discussion on ZFS and virtual memory: ZFS Virtual Memory (Jim Salter, jrs-s.net)
• Discussions on ZFS ARC sizing and behavior are also very informative. For example, this Reddit thread offers community insights on ARC and RAM for TrueNAS: TrueNAS amount of ARC/RAM (r/truenas)