How Much RAM Does a NAS Need for Docker, Plex and VMs?

Quick Summary (TL;DR):
For a basic NAS, 4GB can still be enough if you are mainly serving files and running Plex. Plex itself says 4GB is typically more than sufficient for a normal install. 8GB is the realistic minimum for a modern mixed-use NAS and is also TrueNAS’s current minimum recommendation. 16GB is the best all-round target for most home NAS systems: it gives enough headroom for Plex, several Docker containers, Home Assistant, lightweight databases and an app such as Immich, whose current requirements are 6GB minimum and 8GB recommended. 32GB becomes worthwhile once you run several heavier containers, Immich machine learning, multiple databases, ZFS workloads or one/two useful VMs. 64GB+ is mainly for serious virtualisation, many VMs, large ZFS/iSCSI workloads, AI services and heavier home-lab use. Do not size RAM from storage capacity alone and do not use the old “1GB RAM per 1TB storage” rule as a universal ZFS requirement. Current TrueNAS guidance starts at 8GB for basic operation and then adds memory according to workload, clients, VMs, L2ARC, deduplication and drive count. Also check the NAS’s physical maximum before buying: the current QNAP TS-464 tops out at 16GB, Synology DS925+ at 32GB, while UGREEN DXP4800 Plus supports up to 64GB.

NAS RAM Recommendations at a Glance

RAM	Best fit	Typical workloads
4GB	Basic appliance NAS	SMB/NFS, backups, Plex, very light apps
8GB	Entry mixed-use NAS	Plex + light Docker, basic TrueNAS, Home Assistant
16GB	Best home-NAS sweet spot	Plex + Docker + Immich + databases + light VM
32GB	Advanced home server	Many containers, several databases, multiple VMs, heavier ZFS
64GB+	Home lab / virtualisation	Many VMs, Proxmox, AI services, iSCSI, large caches

The Correct RAM Size Depends on Workload, Not Drive Capacity

A NAS with 80TB of media can need less RAM than a 12TB NAS running PostgreSQL, Immich, Home Assistant, Nextcloud and three VMs.

Memory is consumed by:

• The NAS operating system.
• Filesystem cache.
• Docker containers.
• Databases.
• VMs.
• Plex/Jellyfin metadata.
• Photo-processing/AI services.
• SSD-cache metadata.
• Connected users and file services.

That is why “How many terabytes do you have?” is the wrong first question.

4GB RAM: Enough for a Basic NAS

Four gigabytes is still usable for many proprietary NAS appliances.

It suits:

• File shares.
• PC/Mac backups.
• Basic photo/file apps.
• Plex/Jellyfin Direct Play.
• A very small number of light containers.

Plex’s current support documentation says Plex Media Server does not require large amounts of RAM and that 4GB is typically more than sufficient for ordinary installs.

The bigger Plex bottleneck is normally CPU/GPU capability when transcoding is required.

Where 4GB Starts to Feel Restrictive

Four gigabytes becomes restrictive when several services run at the same time.

• Docker containers competing with filesystem cache.
• PostgreSQL/MariaDB.
• Immich.
• VMs.
• Large photo indexing.
• Multiple simultaneous NAS apps.

At that point the operating system has less room for caching and may begin reclaiming memory aggressively or using swap.

4GB Is Below the Current TrueNAS Recommendation

Current TrueNAS documentation lists 8GB RAM as the minimum hardware recommendation.

So a 4GB appliance may be perfectly good for DSM/QTS/UGOS-style use, but it is not where we would start a new TrueNAS build.

8GB RAM: The Practical Minimum for a Modern Home NAS

Eight gigabytes gives a much healthier baseline.

• Basic NAS services.
• Plex.
• Home Assistant.
• A handful of Docker containers.
• Small databases.
• Basic TrueNAS operation.

It also matches Immich’s current recommended system memory, although running Immich alongside the NAS OS and other containers means 8GB leaves little spare headroom.

Immich Changes the RAM Calculation

Immich’s current requirements are:

• 6GB RAM minimum.
• 8GB RAM recommended.
• 2 CPU cores minimum.
• 4 CPU cores recommended.

Its current TrueNAS application guidance recommends at least 6GB assigned to Immich and suggests going above 8GB when machine learning is enabled.

That does not mean an Immich NAS needs only 8GB total. The host OS, filesystem cache and other services need memory too.

16GB RAM: The Home NAS Sweet Spot

For most enthusiasts buying or upgrading a capable NAS today, 16GB is the easiest recommendation.

It provides enough headroom for combinations such as:

• Plex/Jellyfin.
• Immich.
• Home Assistant.
• AdGuard/Pi-hole.
• PostgreSQL/MariaDB.
• Nextcloud.
• Monitoring containers.
• Download clients.
• A small/light VM.

Sixteen gigabytes also leaves useful memory for filesystem caching instead of forcing every spare megabyte into application survival.

Why 16GB Often Feels Better Than 8GB Even When Nothing “Runs Out”

Linux and ZFS use spare RAM aggressively for cache.

Unused RAM is not necessarily wasted RAM.

Additional memory can keep:

• Filesystem metadata.
• Frequently read files.
• Database pages.
• Application working sets.

in memory, reducing repeated disk access.

32GB RAM: Where NAS Becomes Home Server

Thirty-two gigabytes becomes useful when the NAS is no longer just storing files.

• Many Docker services.
• Two or more VMs.
• Immich plus machine learning.
• Several databases.
• Development environments.
• Large ZFS ARC.
• iSCSI VM storage.
• Multiple simultaneous users.

This is also the maximum supported memory of several current four-bay NAS systems, including the Synology DS925+.

64GB RAM: Serious Home Lab Territory

Most ordinary file/media NAS systems do not need 64GB.

It makes sense when you run:

• Several VMs simultaneously.
• Large development/test environments.
• Proxmox-style virtualisation workloads.
• Multiple memory-heavy databases.
• AI/Ollama services.
• Large iSCSI workloads.
• Many concurrent applications.

Current UGREEN systems such as DXP4800 Plus support up to 64GB, which makes them far more flexible as all-in-one application servers than NAS models capped at 16GB.

Plex Does Not Need Huge RAM

Plex is frequently blamed for needing a large server, but its memory requirement is modest.

Plex’s own current requirement page says 4GB is typically more than sufficient for normal Plex Media Server installs.

For Plex, focus more on:

• CPU transcoding performance.
• Intel Quick Sync / GPU support.
• Codec support.
• Network bandwidth.
• Storage capacity.

RAM becomes relevant mainly because Plex is sharing the host with other applications.

Plex Metadata Benefits from Spare RAM and SSD

A large Plex library can contain a substantial database, posters, preview thumbnails and metadata.

More RAM can cache that data, while placing Plex application data on SSD/NVMe improves random access.

Do not move to 64GB purely for Plex. A small SSD application pool often improves responsiveness more directly.

Docker Itself Is Not the RAM Problem

Docker’s container model has relatively low overhead because containers share the host kernel.

The applications inside the containers consume the RAM.

Docker host
├── Plex            modest RAM
├── Home Assistant  moderate RAM
├── PostgreSQL      workload dependent
├── Immich          6GB minimum / 8GB recommended
├── Nextcloud       workload dependent
└── monitoring      small to moderate

Ten tiny containers can use less RAM than one heavy photo or database service.

Use Actual Container Memory, Not Container Count

After deployment, monitor real usage.

• Host used/free/cache memory.
• Per-container memory.
• Swap activity.
• OOM kills.
• Database cache behaviour.

If the NAS always has several gigabytes available for cache and no swapping/OOM events, adding RAM may not improve anything visible.

Virtual Machines Change Everything

A VM runs its own operating system and reserves/uses substantially more memory than a typical container.

A simple allocation might look like:

NAS / host OS        4–8GB+
Linux VM             4GB
Windows VM           8GB+
Home Assistant VM    2–4GB
other containers     variable

Those are planning examples, not universal application requirements.

Proxmox Makes the RAM Budget Explicit

Current Proxmox VE guidance specifies a minimum of 2GB for the host OS/services plus the memory assigned to guests.

It also notes that ZFS and Ceph need additional memory.

For a host running:

Proxmox host      2GB+
VM 1              4GB
VM 2              8GB
VM 3              4GB
containers        4GB
filesystem cache  headroom

→ 32GB system RAM becomes very reasonable

Do Not Allocate 100% of RAM to VMs

The host still needs memory for:

• Storage services.
• Filesystem cache.
• Networking.
• Backups.
• Management processes.
• Container workloads.

A virtualisation server that technically has enough guest RAM but leaves the host starved is badly sized.

TrueNAS Starts at 8GB

Current TrueNAS hardware guidance lists 8GB as the minimum recommendation for basic operation with up to eight drives.

TrueNAS then recommends adding memory according to workload rather than blindly according to raw pool size.

The “1GB per 1TB ZFS” Rule Is Not a Universal Requirement

This old rule is often repeated without context.

Current TrueNAS guidance starts with 8GB for basic systems and then suggests extra RAM for:

• More drives beyond eight.
• More clients.
• iSCSI workloads.
• Apps.
• VMs.
• Directory services.
• L2ARC.
• Deduplication.

A 100TB archive NAS can work with far less RAM than a much smaller high-performance VM datastore.

ZFS Uses Spare RAM for ARC

ZFS ARC is a memory cache for frequently accessed data and metadata.

That means TrueNAS often appears to “use all the RAM”.

This is normally desirable.

Cache memory can be reclaimed when applications require it, so high reported memory use does not automatically mean the system needs an upgrade.

L2ARC NVMe Cache Also Uses RAM

Adding a large ZFS L2ARC device is not free from a memory perspective.

Current TrueNAS guidance gives a conservative planning estimate of roughly 1GB RAM per 50GB of L2ARC because ARC must hold metadata describing what is cached on L2ARC.

Do not add a multi-terabyte L2ARC to a low-memory TrueNAS box without understanding this overhead.

Deduplication Can Consume Huge Amounts of RAM

ZFS deduplication is a specialist feature and should not be enabled casually.

TrueNAS currently suggests around 5GB RAM per TB of storage for deduplication scenarios that depend on an in-memory deduplication table.

This is where RAM requirements can explode.

Most home NAS users should leave deduplication disabled unless they have measured a real benefit and designed the hardware around it.

iSCSI and VM Storage Need More Memory

TrueNAS specifically recommends at least 16GB for iSCSI-backed VM workloads and 32GB or more for optimal performance.

That matches the practical experience of using a NAS as virtualisation storage: random I/O, metadata and many active blocks benefit from a larger ARC.

More RAM Can Be Better Than NVMe Cache

RAM is much faster than NVMe and has effectively unlimited write endurance.

If you can upgrade from 8GB to 32GB cheaply, that can improve:

• Filesystem cache.
• Database cache.
• Container headroom.
• VM capacity.
• General responsiveness.

before you need an SSD cache.

See Best NVMe SSDs for NAS Cache and Containers once memory is correctly sized.

Memory and NVMe Solve Different Problems

RAM cannot replace persistent SSD storage.

If Docker databases and VM disks need low latency after every reboot, placing them on an SSD/NVMe storage pool remains valuable.

Use:

RAM
→ application working memory
→ filesystem cache
→ VM allocation

NVMe / SSD pool
→ persistent low-latency storage

HDD
→ bulk capacity

ECC vs Non-ECC: Capacity First, Then Protection

If your workloads require 32GB RAM, an 8GB ECC system is not automatically better than a stable supported 32GB non-ECC system.

Meet the workload capacity requirement first, then choose ECC within that capacity where the platform supports it.

Our full guide covers this: ECC vs Non-ECC RAM for NAS and Home Servers.

Current NAS Memory Limits Matter

You cannot upgrade beyond what the NAS platform supports.

Current NAS example	Stock RAM	Official maximum
QNAP TS-464-8G	8GB DDR4	16GB
Synology DS925+	4GB DDR4 ECC	32GB
UGREEN DXP4800 Plus	8GB DDR5	64GB

If you expect several VMs, buying a NAS capped at 16GB can be a bigger limitation than CPU performance.

Buy the NAS for the RAM Ceiling You Need in Three Years

RAM usage tends to grow because users add applications after purchase.

A typical progression is:

Year 1
NAS + backups + Plex

Year 2
+ Home Assistant
+ Docker
+ monitoring

Year 3
+ Immich
+ database
+ VM
+ development tools

If you already know this is where you are heading, a 32GB- or 64GB-capable platform gives much better headroom.

2-Bay NAS RAM Recommendation

A typical two-bay family NAS is usually storage-first.

• 4GB: file serving, backups, Plex.
• 8GB: comfortable file serving + a few apps.
• 16GB: only necessary if the two-bay system is also a serious app server.

4-Bay NAS RAM Recommendation

Four-bay NAS systems are increasingly used as all-in-one home servers.

• 8GB: sensible starting point.
• 16GB: our preferred mixed-use target.
• 32GB: ideal for Docker + Immich + databases + light VMs.
• 64GB: worthwhile only when the platform is genuinely used for virtualisation/heavy apps.

For hardware examples, see Best 4-Bay NAS for Docker, Plex and Family Storage.

6- and 8-Bay NAS RAM Recommendation

Larger NAS systems tend to serve more clients and run more applications.

• 16GB: good minimum for a serious home-lab role.
• 32GB: strong default for mixed storage/apps/VMs.
• 64GB+: useful for many VMs, iSCSI, AI and large-scale Docker.

There is no need to install 64GB simply because the NAS has eight bays. Workload still matters more than disk count.

How to Tell if Your NAS Actually Needs More RAM

• Swap use grows during normal workloads.
• Containers are killed by the OOM killer.
• VMs cannot be allocated enough memory.
• Applications slow badly when several services run together.
• The NAS reports persistent memory pressure.
• Filesystem cache is constantly being squeezed by applications.

High “used RAM” on its own is not proof because Linux/ZFS deliberately use spare RAM for cache.

When More RAM Will Not Help

• CPU is maxed during transcoding.
• Network is limited to 1GbE.
• HDD pool is full.
• VM storage is bottlenecked by random I/O.
• The application itself has a software bottleneck.

RAM should be upgraded because measurement shows pressure or because a planned workload needs it—not because the NAS has an empty memory slot.

A Practical RAM Planning Matrix

Workload	Recommended starting RAM	Notes
File shares + backups	4–8GB	4GB often enough on appliance NAS
Plex only	4–8GB	CPU/GPU matters more than RAM
Plex + several light Docker apps	8–16GB	16GB gives comfortable headroom
Immich + Plex + Docker	16GB	Immich alone recommends 8GB
Immich + ML + many containers	16–32GB	32GB avoids tight sharing
One light VM + Docker	16GB	Depends on guest allocation
Several VMs	32–64GB	Add host + guest requirements
TrueNAS basic file server	8–16GB	8GB current minimum recommendation
TrueNAS + apps + VMs	32GB+	Workload dependent
ZFS iSCSI VM datastore	16–32GB+	TrueNAS recommends 16GB, 32GB+ optimal
AI/Ollama + virtualisation	64GB+	Model/VM dependent

How Much RAM Does a NAS Need? The Bottom Line

4GB is still fine for a simple appliance NAS. File sharing, backups and Plex can run comfortably if you are not stacking applications.

8GB is the practical modern minimum. It matches TrueNAS’s current baseline and gives enough room for a few applications.

16GB is the best default for a mixed Docker/Plex NAS. It provides enough headroom for Immich, databases, Home Assistant and several containers without immediately forcing a second upgrade.

32GB is where a NAS becomes a capable home server. Multiple containers, databases and useful VMs can coexist without constantly fighting for memory.

64GB+ is for deliberate home-lab workloads. Several VMs, large ZFS/iSCSI deployments, AI services and heavy application stacks can justify it; ordinary backups and Plex cannot.

Most importantly, check the platform’s official maximum before purchase. A NAS capped at 16GB can become a dead end if your future plan includes Immich, Docker and several VMs, while a 32GB/64GB-capable model gives room to grow.

Continue the NAS Hardware Series

• Best 4-Bay NAS for Docker, Plex and Family Storage
• Best NVMe SSDs for NAS Cache and Containers
• ECC vs Non-ECC RAM for NAS and Home Servers

Datasheets & External Resources

• Plex – Current Plex Media Server RAM requirements
• Immich – Current hardware and RAM requirements
• Immich – Current TrueNAS application resource guidance
• TrueNAS – Current hardware and memory-sizing guide
• Proxmox VE – Current host/guest memory requirements
• QNAP TS-464 – Current memory specification
• Synology DS925+ – Current memory specification
• UGREEN DXP4800 Plus – Current memory specification