Mixing Hard Drives in Synology NAS: What You Need to Know

When setting up a Synology NAS, most users begin with a simple configuration. Perhaps you started with just two drives, planning to upgrade as your storage needs increased. Or maybe you have a few spare hard drives from older systems that you are tempted to use for your NAS.

Here's the thing: adding drives of different sizes or types to your NAS is not as DIY as it might seem. While it is technically possible, there are some important things to consider before you mix drives in your Synology NAS.

In this guide, we will walk you through the key points you need to know, including how mixing drives works, the pros and cons, and how to manage this process safely and effectively.

Why Users Consider Mixing Drives in a Synology NAS

Before we get into the technical details, let's take a step back and understand why many individuals consider mixing drives in their NAS systems.

Gradual Storage Expansion

Many users start with a few drives and only realise they need more space later. Rather than replacing every drive in the system, it is often more cost-effective to simply add larger drives alongside the existing ones. Synology's systems are known for being flexible, allowing for gradual upgrades over time.

Budget-Friendly Approach

High-capacity drives can be quite expensive, especially NAS-grade models built for 24/7 operation. Mixing drives enables you to expand your system bit by bit, instead of paying a large sum all at once.

Reusing Old Drives

If you have older drives lying around that are still in good health, it makes sense to repurpose them in your NAS rather than let them go to waste. Many users start with what they have before investing in new hardware.

Temporary Storage Requirements

Sometimes you just need to temporarily increase storage for specific tasks, such as moving files, backing up older devices, or handling large short-term projects. Using mixed drives for these purposes can make good practical sense.

Testing Different Drive Setups

Some users mix drives to experiment with different storage configurations before fully committing to a long-term solution. By using a variety of existing drives, you can explore RAID types, backup strategies, and performance settings without making major financial investments upfront.

Is It Safe to Mix Hard Drives in Synology NAS Systems?

Technically, yes, using different drives is generally safe in Synology NAS systems, but it depends on how you approach it and what you expect from your setup.

Synology Hybrid RAID (SHR): Designed for Flexibility

Synology offers a feature called Synology Hybrid RAID, or SHR for short. This is a proprietary RAID management system specifically designed to accommodate different drive sizes.

SHR is ideal for users who want to gradually increase their storage without the strict limitations of traditional RAID systems. It works by automatically allocating available space and managing redundancy, even with mismatched drives.

The key advantage of SHR is that it makes mixing drives with different capacities easy, allowing you to maximise usable space while maintaining redundancy and data protection.

Standard RAID: Less Flexible with Mixed Drives

If you prefer to use traditional RAID types such as RAID 1, RAID 5, or RAID 6, you will face more limitations. In these setups, the system will only use the storage capacity of the smallest drive in the array. This means that larger drives will have significant portions of their storage go unused.

For example, if you have a RAID 5 configuration with drives of 2TB, 4TB, and 8TB, only 2TB of each drive will actually be used, and the rest of the space on the larger drives will be wasted.

Important Considerations Before Mixing Drives

While Synology Hybrid RAID (SHR) can simply add drives of different sizes, it is still important to approach this process carefully. Many users are tempted to throw any old drive into their NAS, but doing so without proper planning can lead to wasted space or even increased risk of drive failure.

Storage Wastage:

One of the most common pitfalls when mixing drives is inefficient use of storage capacity. Even with SHR, which is far more flexible than traditional RAID systems, there are limits to how much capacity you can actually use.

SHR works by balancing available space across all drives while ensuring redundancy, but it cannot fully use mismatched capacities beyond a certain point. In simple terms, the system will often only utilise the available space on a larger drive once other smaller drives have been upgraded to match it.

If you install drives with vastly different capacities, such as mixing a 500GB drive with an 8 TB HDD NAS, much of the larger drive's space will remain unusable until you replace or upgrade the smaller drives in the pool.

Practical Tip: Aim to mix drives with capacities that are reasonably close. For instance, pairing a 4TB drive with an 8TB drive is generally a smart choice, as the difference is manageable, and future upgrades can help unlock full capacity.

Performance Differences:

Another major factor to consider is performance. Hard drives differ in speed, and these differences can have a noticeable impact on how your NAS functions.

Drives from different generations or manufacturers may have varying rotational speeds (measured in RPM), differing cache sizes, and even different interface speeds, such as SATA II versus SATA III. If your NAS contains a mix of fast and slow drives, the entire storage system often slows down to the pace of the slowest drive in the array.

Practical Tip: Where possible, mix drives with similar performance ratings. Avoid combining slow legacy drives with newer, faster ones, particularly if you rely on your NAS for high-speed tasks like video editing or running virtual machines.

Want to take your Synology NAS performance even further? Learn how to boost speed and efficiency in our guide to improving Synology NAS performance with the right SSD.

Drive Health and Reliability:

Drive health is one of the most critical aspects of maintaining a stable NAS, especially when mixing older and newer drives. While it may seem like a good idea to reuse spare drives from previous systems, this comes with risks.

Synology's DiskStation Manager (DSM) includes built-in tools for monitoring drive health, such as SMART tests, which can alert you to failing sectors, temperature issues, or other warning signs of imminent failure.

Practical Tip: Always run a full SMART test before adding a drive to your NAS. Avoid using drives that have high error counts or poor health indicators.

Drive Compatibility:

Another often-overlooked consideration is drive compatibility. Synology publishes an official compatibility list for every NAS model, showing which drives have been tested and verified for optimal performance and reliability.

Practical Tip: Always check Synology's official compatibility list before purchasing or installing drives in your NAS. Stick to NAS-rated drives like WD Red or Seagate IronWolf for long-term reliability and better performance in multi-drive systems. You can also explore drives tailored for Synology NAS drives for enhanced compatibility.

Add Drives to Expand Synology NAS Pool Capacity

Synology has some clear rules on how drives can be added to an existing storage pool. Here is what you need to know:

RAID Compatibility

To expand a storage pool by adding drives, your NAS must use one of the following supported RAID types:

Drive Type Restrictions

Drive Size Recommendations

For SHR, the new drive must be at least as large as the largest drive already in the storage pool to maximise available capacity.

For RAID 1, RAID 5, RAID 6, and RAID F1, the new drive must be equal to or larger than the smallest existing drive.

How to Add a New Drive to Your Synology NAS (Step-by-Step)

You can add new hard drives by following the steps given below:

Once completed, your storage pool will be rebuilt, and additional space will become available once the rebuild is finished.

Expanding Your Storage Volume After Adding Drives

Once new drives are added and the storage pool has been expanded, you may also need to expand your storage volume.
In single-volume storage pools, this happens automatically once the pool has been expanded. In multi-volume storage pools, you may need to manually expand each volume after increasing the pool's capacity. Synology's DSM provides a simple wizard for this process.

Once you’ve upgraded your storage, make sure you can easily access your files from anywhere on your network. Read our complete guide on how to access your Synology NAS from the network to set up secure NAS access across your devices.

Can You Mix Hard Drive Brands?

Mixing drive brands is generally acceptable in Synology NAS systems, but it is recommended to add drives with similar specifications, such as RPM, cache size, and NAS-specific firmware optimisations.

For consistent performance and reliability, Synology encourages the use of its own branded drives and models where possible. However, if you do choose to mix brands, make sure that the drives you combine are fully compatible with your Synology NAS and offer similar speeds and features. If you're considering external upgrades, options like an external hard disk may also suit some storage needs.

Is Mixing Hard Drives Right for You?

Mixing drives in a Synology NAS can work brilliantly for some users but may cause more trouble than it is worth for others. The key is to evaluate your needs carefully and understand how mixing drives could affect your system's performance and flexibility. Here is a quick overview of common user types and recommendations:

• If You are a Home User or Media Enthusiast:

Mixing drives can work very well for most home users, particularly those who use their NAS for storing movies, music, personal photos, or household backups. Synology Hybrid RAID (SHR) makes it easy to combine drives of different sizes and gradually expand storage as needed.

Why it works:

Things to watch out for:

• If You're a Small Business User

While mixing drives can offer flexibility, most small business users are better off using matching drives across their NAS setup. Uniform drives reduce the risk of unexpected slowdowns or compatibility issues and make troubleshooting much easier if something goes wrong.

Learning about storage technologies or maximising older hardware can benefit greatly from mixing drives. For those who regularly tinker with their setups or want to stretch every bit of storage potential, mixing drives is a great way to reuse spare drives and get more value from existing components.

• If You're a Creative Professional:

Creative professionals typically need fast, consistent access to large files, and any slowdown or unexpected drop in performance can disrupt workflows. While adding extra drives to boost capacity might seem convenient, mixing drives may cause inconsistent performance, particularly if slower or older drives are involved.

Conclusion

Adding a combination of drives of different sizes and speeds in a Synology NAS can be a smart, practical way to expand overall storage capacity. Thanks to Synology Hybrid RAID, it is easier than ever to combine drives of different sizes without sacrificing data protection. Whether you're setting up a Synology NAS DS923+ or any other option from the best Synology NAS range, planning carefully ensures long-term success.

However, it is equally important to recognise where mixing drives may not be the best solution. In business environments or creative workspaces where speed, stability, and predictability are essential, sticking with uniform, NAS-rated drives is usually the wiser route.

No matter which approach you take, the rule of thumb is this: always plan ahead. Keep your drives healthy, back up your critical data regularly, and use compatible, reliable hardware wherever possible.

Always keep in mind that RAID is not a replacement for proper backups. Make sure you have copies of your critical data elsewhere, whether on an external drive or in the cloud.

Want to Expand Your Synology NAS?

At Box.co.uk, we stock a wide selection of NAS-ready Synology drive solutions. Whether you are building your first NAS or expanding an existing one, we have everything you need for a reliable storage solution.

Explore our full range of NAS-compatible hard drives here: Explore Synology NAS UK Store.

Ready to do more with your NAS? Set up your Synology NAS as a personal cloud for secure, anywhere-anytime access to your files.

Mixing Hard Drives in Synology NAS: FAQs

Can you mix drive brands in Synology?
Yes, you can mix drive brands in Synology NAS systems. However, it's recommended to use drives with similar specifications such as rotational speed, cache size, and intended workload to ensure consistent performance and system stability. For higher-end models, Synology may require their own branded drives for full compatibility and warranty support.

Can I use any HDD in Synology?
Not all HDDs are supported. Synology NAS devices are designed to work with drives listed on their official compatibility list. Using supported drives ensures optimal performance, reliability, and access to Synology's technical support.

Do NAS drives have to be the same brand?
No, NAS drives do not have to be the same brand. However, for better compatibility and consistent performance, it's advised to use NAS-rated drives from reputable brands. For some enterprise and high-end NAS models, Synology may require the use of its own certified drives.

Are all hard drives compatible with NAS?
While it's technically possible to use standard desktop hard drives in a NAS, it is not recommended. NAS-grade drives are specifically engineered for continuous, 24/7 operation and high data workloads. Regular hard drives lack the durability, vibration resistance, and firmware optimisations required for NAS systems.

Can I mix drive sizes in a NAS?
Yes, you can mix drive sizes in a NAS, especially if you use Synology Hybrid RAID (SHR). SHR allows drives of different sizes to be combined while optimising storage space and maintaining redundancy. However, in traditional RAID configurations, the storage capacity is limited by the smallest drive in the array.

Can you mix SSD and HDD in Synology?
Mixing SSDs and HDDs within the same storage pool is generally not recommended in Synology NAS systems. However, you can use SSDs for caching alongside HDD-based storage pools to boost read/write speeds while maintaining bulk storage on traditional hard drives.

What is the best drive configuration for NAS?
For most home users, RAID 1 and RAID 5 are considered the best options for a NAS. RAID 1 offers simple mirroring for excellent redundancy, while RAID 5 provides a balance between storage capacity, performance, and fault tolerance, making it ideal for systems with three or more drives.

Can you put any hard drive in a NAS?
Technically, yes, but it's not recommended. Only NAS-rated hard drives should be used in a NAS environment. These drives are designed for continuous operation, with firmware optimisations for RAID environments and better protection against vibration and heat.

Can you combine two hard drives together?
Yes, two hard drives can be combined using software solutions such as Windows Disk Management, Storage Spaces, or third-party partitioning tools. In NAS systems, combining drives is typically done through RAID configurations or storage pooling features like Synology Hybrid RAID (SHR).