TrueNAS RAM and ARC Calculator

How the TrueNAS RAM estimate works

Start by counting populated data-drive bays, the apps expected to be active together, and simultaneous share users. Enter zero apps for a storage-only scenario. The calculator accepts two to sixty drives, zero to fifty apps, and zero to two hundred users. Its purpose is to make the assumptions easy to compare before you check the needs of a specific deployment.

The model starts with 8 GB plus 1 GB for each drive beyond eight, following the basic guidance in the TrueNAS 25.10 hardware guide. It then adds an editorial allowance of 1.5 GB per app and 0.5 GB per concurrent user, rounds up to a whole GB, and applies a 16 GB planning minimum. Those workload additions and the 16 GB floor are assumptions of this tool, not requirements published by TrueNAS.

RAM = max(16, ceil(8 + max(0, drives - 8) + 1.5 × apps + 0.5 × users))

A worked memory example

With the default twelve drives, the drive allowance is 12 GB. Twelve apps add 18 GB, and fifteen concurrent users add 7.5 GB. The sum is 37.5 GB, rounded to a 38 GB planning allowance. That result is arithmetic from the stated inputs. It is not a memory-module shopping list, a benchmark or a guarantee that a particular collection of apps will fit.

App count is only a shortcut. A database, a media service and a small utility can need very different amounts of memory. Replace the generic allowance with each application's documented requirements when preparing a final plan. Inventory the deployment details using the app migration guide.

What the ARC figure means

The ARC tile takes half the calculated RAM allowance and rounds it to a whole GB: 19 GB in the default example. This is an illustrative budget, not a prediction of the system's working set or a configured ARC maximum. The tool neither reads nor changes TrueNAS settings.

OpenZFS documents ARC limits through parameters such as zfs_arc_max and zfs_arc_min. Defaults and behaviour depend on the platform and release; the OpenZFS parameter reference supplies that context. For the requirements discussion, read how much RAM TrueNAS needs.

Network throughput and other limits

The network tile divides one link's gigabits per second by eight to show decimal gigabytes per second. A 10 Gbps link gives a theoretical 1.25 GB/s. Protocol overhead and the work performed by disks, clients and applications reduce achievable file-transfer throughput. This calculation does not combine ports or estimate measured performance.

Pool capacity, parity, deduplication, virtual machines and detailed per-app memory limits are outside this model. Use the TrueNAS pool capacity calculator for usable storage arithmetic. See the HBA and boot drive guide for disk attachment and recovery preparation, or return to all operations tools.