SSD Caching for NAS: Boosting Speed and Efficiency

In the world of DIY NAS builds, speed and responsiveness are often just as important as storage capacity. One of the most effective ways to boost the performance of your NAS is by adding SSD caching. Whether you’re streaming media, running virtual machines, or hosting cloud services at home, SSD cache can make a noticeable difference.

In this guide, we’ll explore what SSD caching is, when it makes sense, which SSDs are best suited for caching, and how to set everything up. Whether you’re using TrueNAS, Unraid, or OpenMediaVault, this article will help you decide if SSD caching is right for your build.

What Is SSD Caching?

SSD caching involves using a solid-state drive (SSD) as a high-speed buffer between your NAS’s RAM and slower spinning hard drives (HDDs). Instead of fetching data from the HDD every time, frequently accessed files are temporarily stored on the SSD, significantly reducing access times.

Think of it like a fast lane on a highway: data that’s used often travels through the SSD (fast lane), while less frequently accessed data remains on the HDD (main road).

Beyond faster access times, SSD caching also reduces the number of read/write operations on your hard drives, minimizing mechanical wear. Additionally, with more data served from the SSD, your HDDs can spin down more frequently, leading to lower power consumption and improved energy efficiency.

Types of SSD Cache and Caching Modes

Read Cache

Stores frequently accessed files, reducing read latency. Ideal for streaming media or frequently used documents. This also benefits self-hosted apps like Nextcloud, Immich, or Paperless, where documents, photos, and scanned files remain on the NAS but still load quickly through the cache, mimicking local performance for a smoother user experience.

Write Cache

Temporarily stores data before writing it to the HDD. Since SSDs can receive and write data much faster than mechanical hard drives, this significantly accelerates file transfers. The cached data is then written to the HDD in the background, typically during idle times or overnight. This not only improves the user experience with fast write acknowledgments but also helps reduce disk contention and improves responsiveness in multitasking NAS environments.

Read+Write (Hybrid)

Combines both approaches. Best suited for applications with both heavy read and write operations, such as virtual machines, databases, or development environments.

Benefits of SSD Caches

Improvement of a SSD Cache

3x–10x faster read speeds (especially for small files)

Faster file transfers and write acknowledgments

Snappier UI and file browsing

Enhanced performance with Docker, databases, and VMs

Best Use Cases for SSD Cache

Media servers like Plex or Jellyfin

File servers with frequently accessed documents

Virtual machines or Docker containers

Cloud storage or office file sharingList item

When not to use SSD Caches

SSD Cache is not ideal for

Backup-only or cold-storage NAS setups

Surveillance or archival data

When Not to Use SSD Cache

On budget NAS builds with limited slots or power

When using only cold or archival storage

With low-end DRAM-less SSDs (which can wear out quickly)

In setups without proper backup or a UPS (write cache may risk data loss)

Note: Cold storage refers to infrequently accessed data such as backups, old media collections, or compliance-related documents. These files are rarely read or written, making speed less critical than reliability and capacity.

Choosing the Right SSD for Caching

When selecting an SSD for caching, consider the following:

Endurance

Look for high TBW (terabytes written) or DWPD (drive writes per day). NAS environments often involve frequent write operations.

NVMe vs SATA

NVMe SSDs offer much higher performance than SATA but require compatible hardware.

Capacity

SSD cache sizes typically range from 128 GB to 4 TB. A general rule: 10% of your total NAS storage capacity is a good starting point.

Power Loss Protection

Prevents data loss in case of a power failure. This is especially important for write cache setups—though a reliable UPS can also mitigate this risk.

Recommended SSDs for NAS Caching

For a current and always up-to-date list of recommended SSDs for caching, please visit our hardware guide section on the website. There you’ll find detailed comparisons, interface types, and curated picks for every budget and use case.

Hardware Components Guide

View Components Guide

How to Set Up SSD Cache on Your System

TrueNAS

Use SSDs as L2ARC (read cache) or SLOG (write cache)
Configure under: Storage > Pools > Cache Devices

Unraid

Assign SSDs to the cache pool
Configure shares to use cache (yes / prefer / only)

OpenMediaVault (OMV)

Install the flashmemory plugin to reduce unnecessary writes
Advanced users can configure SSD caching manually with mergerfs

Conclusion

SSD caching is a powerful way to accelerate your NAS without a complete hardware overhaul. Whether you’re running a media server, managing files, or hosting VMs, it delivers a noticeable performance boost. Choosing the right SSD and configuration is key. Visit our hardware component guide to find the best-tested SSDs for speed, endurance, and reliability.

Looking to optimize your NAS? Head over to our Golden Builds or browse the best SSDs for caching in our hardware recommendations. Don’t forget to support our work by purchasing through our affiliate links! This will help us maintain the blog and provide future content. Huge thanks in advance for considering.

Frequently Asked Questions

Find answers to commonly asked questions about SSD caches on NAS.

Can I use a USB SSD as cache?

No. USB drives lack the performance and stability required.

Is SSD cache worth it for Plex?

Yes, especially for large libraries and frequent transcodes.

What happens if my cache SSD fails?

Read cache loss isn’t critical. Write cache loss can cause data corruption unless you use write-through mode or a UPS.

How much SSD cache do I need?

A good starting point is 10% of your total NAS storage. Power users and VM hosts may benefit from more.

Can I use a DRAM-less SSD for caching?

It’s possible, but not recommended. DRAM-less SSDs generally have lower performance and endurance.

Does SSD cache help with Nextcloud or Immich?

Absolutely. SSD caching greatly improves responsiveness for accessing photos, documents, and syncing data in apps like Nextcloud, Immich, and Paperless.

Do I need a UPS if I use write caching?

Yes. Without a UPS, you risk data loss during power outages if the write cache hasn’t been flushed.

Can I use multiple SSDs for cache?

Yes. Some NAS platforms support multiple cache drives in RAID or tiered setups for improved performance and redundancy.

Still have a question?

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