TrueNAS hardware guide: what ZFS really needs

RAM: ignore the 1 GB-per-TB myth

The rule '8 GB plus 1 GB per TB' dates from the FreeNAS era and is quoted far past its usefulness. OpenZFS 2.x sizes its ARC cache dynamically, so what ZFS needs tracks the size of your actively read data, not the raw pool. A 120 TB archive read occasionally needs far less than the rule's 128 GB; a busy pool of VMs can want more per TB. Size it with the TrueNAS RAM calculator, which shows both the rule and the realistic figure.

ECC: recommended, and here is why

ECC memory catches and corrects single flipped bits before they are written. In a box that runs 24/7 and may hold your only copy of some files, that is the safeguard worth having, and it is why experienced ZFS builders insist on it. It is not mandatory, TrueNAS runs fine on non-ECC, but if your board and CPU support ECC, use it.

The catch is platform: the popular N100 has no ECC. For ECC you step up to an Intel Xeon E, a Ryzen with an ECC-capable board, or an embedded Ryzen like Synology uses. That is a real cost-and-complexity jump, which is the honest trade-off to weigh.

CPU, HBA and boot

• CPU: for a file server, almost anything modern is enough; the N100 handles SMB and a few apps. For many VMs or heavy Plex transcoding, step up to a Pentium, Core-i or Ryzen.
• Drive connection: use the chipset SATA ports first. If you need more, an LSI/Broadcom HBA in IT mode (9207-8i, 9300-8i) is the reliable choice: avoid cheap port multipliers.
• Boot: a small SSD, never a USB stick. TrueNAS SCALE writes constantly and sticks fail.