TrueNAS RAM Requirements by Workload

TrueNAS needs 8 GB of RAM minimum, the official figure for basic operation with up to eight drives. Add 1 GB per drive past eight, 2 GB for Active Directory or LDAP, and plan 16 to 32 GB for iSCSI VM storage. A home NAS running apps wants 16 GB as a floor and 32 GB to be comfortable.

Those figures come from the hardware guide for 25.10 “Goldeye”, the release the software status page recommends for general users (25.10.7, checked September 2026). CPU, HBA, drive, boot device, networking, power supply, and cooling choices are covered in the TrueNAS hardware buying guide.

TrueNAS RAM requirements at a glance

TrueNAS uses more RAM at idle than a Synology or QNAP box running a similar drive count, and that’s by design rather than bloat. The SCALE Hardware Guide explains that TrueNAS shares memory across sharing services, apps, virtual machines, and, most notably, ZFS’s read cache. RAM “rarely goes unused on a TrueNAS system,” and that’s a feature: unused RAM is a cache miss you didn’t have to take.

Official figures below are from the 25.10 hardware guide; practical targets are editorial, not iXsystems policy.

Read that dedup line again if you’re planning to enable it: 5 GB per TB is not a typo, and it’s the single biggest RAM multiplier on this whole list. A 20 TB pool with dedup on wants on the order of 100 GB of RAM just for the dedup table, separate from ARC. Most home users should leave dedup off and rely on compression instead, which costs CPU cycles, not gigabytes of RAM.

TrueNAS RAM calculator: find your number in six steps

There is no official TrueNAS RAM calculator, but the hardware guide’s rules add together, so a pencil does the job:

1. Start at 8 GB for basic sharing on up to eight drives.
2. Add 1 GB for each drive past eight. A 12-bay chassis adds 4 GB.
3. Add 2 GB if the NAS joins Active Directory or LDAP.
4. Raise the base for iSCSI. If the box serves iSCSI storage to a hypervisor, this guide uses the official 16 GB (good) or 32 GB (optimal) as the starting figure in place of 8 GB.
5. Add what runs on TrueNAS itself: the memory assigned to each VM, plus what your apps use.
6. Add cache and dedup overhead: 1 GB per 50 GB of L2ARC, and 5 GB per TB of deduplicated storage.

Round up to the next capacity your motherboard takes as a matched kit. The leftover isn’t wasted; ZFS hands it to the ARC. Five common builds, worked through (the “buy” column is editorial):

Can TrueNAS run on 4 GB of RAM?

Yes, it installs and runs, but 4 GB is half the documented minimum and a poor home for data. The 25.10 hardware guide concedes that TrueNAS “hosts SMB shares and replicates TBs of data with less” than 8 GB, then adds that the team recommends the minimums “for better performance and fewer issues.”

Older documentation was blunter. The FreeNAS 11.3 user guide said “Do not use FreeNAS to store data without at least 8 GiB of RAM,” and noted that its minimums “are based on feedback from many users.”

On 4 GB, middleware, sharing services, and the ARC compete for the same few gigabytes, so the cache that makes ZFS fast is squeezed first and apps or VMs have nowhere to run. A test VM gets no exemption: the 25.10 install guide asks for “at least 8192MB (8GB)” there too. Bring an old 4 GB machine to 8 GB, ideally 16 GB, before creating a pool.

TrueNAS and FreeNAS minimum requirements by release

RAM is the one line of the TrueNAS minimum spec that has stayed put. The CPU and boot device minimums have shifted between releases; 8 GB has not:

Every TrueNAS-era guide in that table (CORE 13.0 onward) also lists two identically sized devices for a single storage pool. When the 25.10 hardware guide and install guide disagree on the boot device, give it 20 GB or more and the question goes away.

On CPU, the hardware guide favours “a higher-frequency CPU with fewer cores” for SMB-only workloads, more cores for encryption and virtualization, and AES-NI for faster encryption. Model-by-model picks are in best CPU for TrueNAS SCALE.

FreeNAS was renamed TrueNAS CORE, which the software status page now calls “no longer under active development.” Its RAM rules match the current ones, so a machine sized for FreeNAS is sized for TrueNAS 25.10; the move is covered in how to migrate from TrueNAS CORE to SCALE.

Sizing RAM by what you’re actually running

File sharing only (SMB, NFS, no apps)

8-16 GB covers this comfortably for a small home setup of four to eight drives. Stick close to the official 8 GB floor plus the per-drive adjustment, and you’ll be fine unless you’re serving a lot of concurrent clients. The hardware guide’s only advice for those is to add extra RAM as more clients connect.

TrueNAS SCALE apps (Plex, *arr stack, Nextcloud, etc.)

Budget the base file-sharing RAM, then add whatever the apps themselves need on top. Apps run in containers and use memory outside the ARC, which shrinks to make room for them. 16 GB is a realistic minimum once you’re running more than one or two lightweight apps; 32 GB gives real headroom for a stack like Plex plus Nextcloud plus a couple of *arr containers without starving the ARC. The TrueNAS SCALE apps guide covers the datasets and install steps.

iSCSI storage for virtual machines

When TrueNAS is the storage target for VMs running on another hypervisor, the official guidance is to plan for at least 16 GB of RAM for good performance and 32 GB or more for optimal performance. Use that figure as the base in place of 8 GB, then add the other rows of the table on top.

Virtual machines hosted on TrueNAS

This is where RAM requirements jump the most. The hardware guide says to “add more RAM for virtual machines with a guest operating system and application RAM requirements.” VMs reserve their allocated memory directly, on top of whatever TrueNAS itself and ARC need, so this isn’t optional headroom. It’s a hard subtraction from what’s left for caching.

Deduplication

Don’t turn it on below 32-64 GB of total system RAM unless your pool is very small. At 5 GB per TB, dedup RAM costs scale faster than most home users expect, and the payoff (space savings) is workload-dependent. The 5 GB figure is the conservative one: the TrueNAS deduplication reference says pools with dedup ratios of 3x or more “might only need 1-3 GB of RAM per 1 TB of data,” and Fast Dedup, introduced in OpenZFS 2.3.0, adds a quota that stops the dedup table growing without limit. Compression (usually lz4 or zstd, on by default in modern TrueNAS) gets you most of the practical benefit without the RAM tax.

Directory services (AD/LDAP)

Add a flat 2 GB on top of whatever your base workload requires, for the Winbind cache.

Where your RAM actually goes: the ARC

Whatever RAM isn’t claimed by services, ZFS will grab for the ARC (Adaptive Replacement Cache), its in-memory cache of recently and frequently read blocks. This is why TrueNAS looks like it’s “using” most of your RAM even when the system is nearly idle. That’s cache doing its job, not a leak, and it gets released instantly if something else needs it.

On current releases the ARC may grow into nearly all of it. When zfs_arc_max is left at 0, the OpenZFS zfs(4) man page sets the ceiling at the larger of total RAM minus 1 GiB or 5/8 of total RAM. Linux had used a half-of-RAM cap until OpenZFS PR #15437 aligned it with FreeBSD, and TrueNAS made the equivalent change in 24.04, whose version notes say ARC allocations now “behave identically to TrueNAS CORE.” Forum posts saying SCALE’s ARC stops at half your RAM describe releases before 24.04. The other ARC tunables are listed in the OpenZFS module parameters documentation. You can check what your system is actually running with:

arc_summary | head -20

The practical takeaway: more RAM directly increases your ARC hit rate, and ARC hits are served in microseconds versus milliseconds from disk. If you’re chasing read performance on a home NAS, adding RAM is almost always a better first move than adding an L2ARC SSD, because ARC has no read/write overhead penalty that L2ARC does.

Where the “1 GB per TB” rule actually comes from

If you’ve spent any time in NAS forums, you’ve seen the rule “1 GB of RAM per TB of storage.” It is repeated constantly, but for most users it answers a different question from the one they are asking.

The rule is old FreeNAS guidance, and iXsystems retired it years ago. The FreeNAS 11.3 user guide calls it “an old, somewhat overstated guideline” and lists deduplication separately, at 5 GiB per TB. Current TrueNAS hardware guides drop capacity-based sizing altogether and count drives, services, and features instead. Without dedup enabled, pool capacity has almost nothing to do with how much RAM you need: a 4-drive 40 TB media pool serving Plex to two people doesn’t need meaningfully more RAM than a 4-drive 8 TB pool doing the same job. What actually drives your RAM requirement is your working set: how much data you touch repeatedly, and how many services are competing for cache space at the same time.

If you want a rule of thumb that isn’t cargo-culted, size RAM for the workload (file sharing, apps, VMs, dedup) using the categories in this guide, not for raw pool capacity.

ECC vs. non-ECC: a related but separate question

RAM capacity and RAM type are two different decisions. ECC (Error-Correcting Code) RAM detects and corrects single-bit memory errors before they get written to disk. That matters to ZFS because its checksums are computed in memory, so a silent bit-flip before checksum time can produce a “valid” checksum for already-corrupted data. The 25.10 hardware guide doesn’t make ECC a requirement. Summing up the long debate, it says most users “strongly recommend ECC RAM as another data integrity defense,” and it acknowledges that many systems run without it. If you’re choosing a platform and ECC support is on the table, prioritize RAM quantity first, then ECC if your budget and motherboard support it.

The short version

Start from the official 8 GB floor and add only for what you run. For most home builds today, that lands you at 16 GB as a realistic working minimum and 32 GB as a comfortable target that leaves room for ARC to actually do its job. Buy RAM before you buy a bigger CPU; on a NAS, memory is almost always the better upgrade.

FAQ

Is 8 GB of RAM enough for TrueNAS?

Yes, for basic SMB or NFS file sharing on up to eight drives, which is exactly what the official 8 GB minimum covers. It leaves little room for apps, VMs, directory services or a useful ARC, though, so most home builds that plan to run anything beyond plain shares should start at 16 GB instead.

Is 32 GB of RAM overkill for TrueNAS?

Not if you run apps or VMs. For a four-drive box that only serves files, 32 GB is well above the official 8 GB minimum, but ZFS spends the surplus on ARC read cache rather than leaving it idle. With a Jellyfin, Nextcloud and VM stack, 32 GB is the comfortable target rather than overkill.

How much RAM should a TrueNAS VM get?

At least 8 GB. The TrueNAS 25.10 install guide asks for a minimum of 8192 MB when TrueNAS runs as a virtual machine, the same floor as bare metal, and says a 20 GB virtual disk is enough for booting. Size the rest as on bare metal, adding RAM for extra drives, directory services, and apps.

Can I add more RAM to TrueNAS later?

Yes. Shut down, install the modules, and boot; unless you set a custom zfs_arc_max tunable, nothing needs changing. When zfs_arc_max is 0, the default, OpenZFS sizes the ARC ceiling from installed memory, so the extra capacity goes to cache and services automatically. Match new modules to the existing ones and check the board’s supported memory list.