TrueNAS HBA and Boot Drive Guide: IT Mode, Sizing, Pitfalls

A TrueNAS box needs an x86_64 Intel or AMD CPU, at least 8 GB of RAM, a separate SSD boot device of at least 20 GB and two identically sized data disks. Connect the data disks through onboard SATA or a Broadcom (LSI) SAS HBA flashed to IT firmware, never through a hardware RAID volume.

Those minimums come from the current TrueNAS hardware guide and the 25.10 installation guide, which both set the boot floor at 20 GB. The older 25.10 hardware guide page still lists a 16 GB SSD, so plan on 20 GB for 25.10.7, the release the software status page recommended for general users in September 2026.

For a full build walkthrough, see TrueNAS Guide’s hardware requirements; for a longer RAM discussion, how much RAM TrueNAS needs; for an apps workload estimate, the TrueNAS RAM and ARC Calculator.

TrueNAS hardware requirements at a glance

TrueNAS HBA: IT mode and direct disk access

The TrueNAS 25.10 hardware guide describes both onboard SATA and SAS HBAs. An HBA adds disk connectivity when the motherboard does not provide enough suitable ports; it is not a requirement to add a separate card to every build.

Keep hardware RAID out of the data path. ZFS manages redundancy and needs access to the underlying disks. A controller label such as JBOD or passthrough is a starting point for checking its behaviour, not proof that every implementation works identically.

Before creating a pool, record the exact adapter model, firmware version and operating mode. Confirm that TrueNAS lists the expected disks individually. Match their serial numbers to physical bays so a future replacement does not depend on guessing which cable belongs to which disk.

Use the adapter vendor’s instructions for its exact board revision when a firmware change is necessary. A reseller’s description is not a substitute for that identification.

Which HBA to buy for TrueNAS

The best HBA for TrueNAS is a Broadcom (formerly Avago, formerly LSI) SAS card from a family the hardware guides name, flashed with the latest IT or Target mode firmware:

Tri-mode driver support still moves with the release: TrueNAS 26 makes the 9500 TriMode driver apply its 2M transfer size limit correctly (NAS-140978). For a RAID controller, the current guide says not to use its RAID facility if the card supports HBA mode.

Check connectors, PCIe fit and cooling

The Broadcom SAS 9300-8i user guide is a useful example of the specification checks involved. It describes eight internal SAS/SATA lanes, two SFF-8643 mini-SAS HD connectors and an eight-lane PCIe 3.0 interface. Those are specifications for that model, not for every card carrying an LSI or Broadcom name.

Build a connection list before ordering:

The same guide specifies minimum airflow for its thermal limit. A passive heatsink still needs moving air. Treat an adapter removed from a server as a component with documented installation requirements, rather than assuming a quiet desktop case provides equivalent cooling.

These checks connect the controller decision to the boot-drive decision: reserve the intended boot connection when allocating motherboard ports and expansion slots.

TrueNAS boot drive size: minimum and update space

Use a boot SSD of at least 20 GB; the hardware guide adds that a bigger device provides room for more boot environments. It does not mean a larger boot device provides a larger data pool. Keep the operating-system device separate from the disks intended for application data and shares.

Pick flash on SATA, SAS or NVMe. The 25.10 version notes do not recommend USB boot devices, and TrueNAS 26 drops USB boot as a supported configuration (NAS-140745). The hardware guide says USB drives and SATA DOMs vary too widely in quality, and that all pre-built TrueNAS systems ship with M.2 boot devices.

Allow space for updates and retained boot environments. The 25.10 Boot screen reference exposes boot-pool size, used space, device status and the space associated with each environment. Check those values before an upgrade instead of treating a particular SSD capacity as a universal lifetime allowance.

Boot environments provide operating-system restore points. The Keep setting controls whether an environment is eligible for automatic cleanup when an update needs space. Retaining every environment increases the space that must remain available.

A mirrored boot pool is optional. The same Boot screens use Attach to mirror the boot pool onto a second device, which must be equal to or larger than the current one, and they scrub the boot pool every seven days by default.

A purchasing decision therefore has two parts: meet the release’s installation requirement, then choose how much room to leave for the environments you intend to retain. This is a planning allowance, not a performance rating or a measured endurance claim.

Recovering after a boot-drive failure

The separate boot device is useful only if the configuration can be recovered. The configuration backup documentation explains why exports should include the password secret seed: protected database fields need it when restoring onto another operating-system device.

Keep that export securely off the NAS and refresh it after significant configuration changes. Keep dataset encryption keys and passphrases available separately. A system configuration export is not a copy of the files stored in the data pool.

The installation documentation describes recovery through a clean installation, configuration restoration and access to the existing data. Identify the replacement boot device carefully before installing; the data disks are not installation targets.

Record the installed release alongside the backup. During recovery, check the destination release’s compatibility before restoring settings or importing storage. Being able to locate the backup, identify the boot device and distinguish it from the data disks matters more than memorising a sequence of screen labels.

TrueNAS RAM requirements

TrueNAS needs 8 GB of RAM at minimum, and the hardware guide scales that by workload. Start at 8 GB and add:

A 12-drive SMB server joined to Active Directory comes to 8 + 4 + 2 = 14 GB, which a 16 GB configuration covers with little left for apps. The TrueNAS ZFS Primer adds a floor for cache devices: do not add L2ARC to a system with less than 32 GiB of RAM, because L2ARC needs RAM to function. On ECC, the guide notes that most users strongly recommend it as another data-integrity defense.

TrueNAS SCALE ARC size

On TrueNAS SCALE 24.04 and later, the ARC can grow to nearly all RAM. The 24.04 version notes say ARC memory allocations behave identically to TrueNAS CORE (NAS-123034), and the Dragonfish release post calls it full memory utilization. With zfs_arc_max at 0, the OpenZFS 2.3 zfs(4) manual sets the ceiling at the larger of total memory minus 1 GiB and five-eighths of total memory.

That is 15 GiB on a 16 GiB system and 63 GiB on a 64 GiB system: a ceiling, not a reservation. To see what the ARC is doing:

1. Open the Dashboard. The Memory widget shows ZFS Cache in fuchsia pink beside Free (blue) and Services (orange).
2. On 25.10, built on OpenZFS 2.3, run arc_summary in the shell. TrueNAS 26 moves to OpenZFS 2.4, where the OpenZFS caching guide names the tool zarcsummary.
3. Run cat /sys/module/zfs/parameters/zfs_arc_max. A result of 0 means the memory-based default applies.

The module parameter guide documents changing that value at runtime; per zfs(4), lowering it below the current ARC size does not shrink the cache until memory pressure does. Before capping the ARC for VMs, note that 25.10.0 lists a fix for ARC memory management conflicts that caused out-of-memory crashes.

Prebuilt TrueNAS boxes: Mini X+, Mini R, R10 and X20-HA

If “TrueNAS box” means hardware iXsystems builds, the current compact models are the Mini X+ and Mini R. The R10 and the X-Series, which includes the X20-HA, are retired Enterprise appliances listed on the product retirement notices page.

A used X20-HA needs more planning than its bay count suggests: the Enterprise HA install guide says HA installs should be guided by Enterprise-level support and need three static IPs, one per controller plus a virtual IP.

Auto TRIM on TrueNAS SSD pools

Auto TRIM is off by default because, per the pool management guide, it can impact pool performance; it only acts on devices that support discard, such as SSDs. To enable it in 25.10:

1. Select Storage to open the Storage Dashboard.
2. On the pool’s Storage Health widget, click Edit Auto TRIM.
3. Select Auto TRIM and click Save.

The setting maps to the OpenZFS autotrim pool property. The zpoolprops(7) manual notes that lower-end devices get most of the benefit from running zpool trim periodically instead, the cautious choice for budget SATA SSDs.

Tiered storage in TrueNAS: fusion pools and TrueNAS 26

Community Edition has no storage tiering feature. Storage Tiering, introduced in TrueNAS 26, is Enterprise-only: a share-level toggle that decides whether new writes land on the flash or HDD tier of a fusion pool. The migration guide warns that it does not support zvols, so iSCSI and Fibre Channel may not benefit.

Every edition gets fusion pools. The 25.10 fusion pool guide says the flash special vdev holds metadata, indirect blocks and deduplication tables, and can accept small file blocks. If it fails without redundancy, the pool becomes corrupted, so match the data vdevs’ protection; in a RAIDZ pool it is permanent. L2ARC and SLOG are not tiers, and OpenZFS states plainly that a SLOG is not a write cache.

Preserve the deployment boundaries before installing apps

The storage-planning decisions below belong in the handoff from controller installation to app operations. They preserve the useful material from the former deployment-planning guide without requiring a second storage overview.

Record the vdev layout. OpenZFS pools distribute data across top-level data vdevs; redundancy is provided within each vdev. Losing a required data vdev can make the pool unavailable even when other disks remain healthy. An HBA with more ports does not change those failure boundaries. Use TrueNAS pool design: RAIDZ versus mirrors for the layout decision.

Give each workload a dataset boundary. Dataset properties include compression, record size and quotas. Properties can be inherited, so record which are deliberately overridden. OpenZFS documents that changing record size affects newly created files rather than rewriting existing ones. Choose properties before loading app data and consult datasets versus zvols when the application needs file storage or a virtual block device.

Choose an access policy with the mount. A container’s user and group need appropriate access to its mounted data. In TrueNAS, Host Path uses storage you identify while ixVolume creates persistent storage on the apps pool. Record both the host location and the path visible inside the container. For client file sharing, follow TrueNAS Guide’s SMB setup.

Keep rollback and backup separate. Snapshots preserve an earlier dataset state on the same storage; they do not survive loss of that storage. Include app data in a separate backup plan and verify that a restored file can be read. A boot configuration export, a dataset snapshot and an independent copy each solve a different recovery problem.

Check the maintenance handoff

Before loading important app data, review the pool’s scrub schedule and the drive-health options available in the installed release. The 25.10 pool management guide explains scheduled scrubs, threshold days and disk status; TrueNAS creates a scrub for each pool that runs every Sunday at 12:00 AM. Confirm that the alert destination is one you monitor, and include a file restore in the deployment checklist.

Once those boundaries are recorded, continue with TrueNAS app migration and Docker operations or the CUPS custom-app walkthrough. Those guides cover the service layer that uses the disks and boot installation prepared here.

FAQ

is 16gb of ram enough for truenas scale?

Usually, for a plain file server. The hardware guide’s 8 GB base plus 1 GB per drive beyond eight reaches 16 GB at 16 drives, or 14 drives with a directory service, which adds 2 GB. For iSCSI storage backing VMs, the guide treats 16 GB as the starting point and 32 GB or more as optimal.

why is truenas using all my ram?

Because the ZFS ARC is doing its job. Since TrueNAS SCALE 24.04, ARC allocation matches CORE, and the OpenZFS default lets the cache grow to total memory minus 1 GiB on systems of 8 GB and up. The Dashboard reports it as ZFS Cache, and the ARC shrinks when apps, VMs or services create memory pressure.

can i use a raid card instead of an hba with truenas?

Yes, if it runs in HBA mode. The hardware guide says not to use a RAID card’s RAID facility when the card supports HBA mode, and Broadcom cards should run IT or Target mode firmware. ZFS manages redundancy itself, so a hardware RAID volume hides the individual disks it needs to see and manage.

can truenas boot from a usb drive?

Avoid it. TrueNAS 25.10 does not recommend USB boot devices and points to SATA, SAS or NVMe flash instead, and the TrueNAS 26 notes state that USB boot is no longer a supported configuration. A small SSD that meets the 20 GB minimum, ideally on M.2 like iXsystems’ own systems, is the practical replacement.