HomeConsumer & SMBNASExpand the Storage Pool Capacity of your Synology NAS

Expand the Storage Pool Capacity of your Synology NAS

In this guide, we will expand the storage pool capacity of your Synology NAS. If you have empty drive slots on your NAS, you install additional drives and add them to an existing storage pool to increase your NAS capacity and performance. 

Installing and configuring additional drives to your Synology NAS is straightforward. In this step-by-step guide, we will explain everything you need to know to carry out this operation. First, we are going to see some caveats and considerations before you expand a storage pool. We also should monitor the condition of the current drives in our NAS and run a S.M.A.R.T. test, and make sure no issues are detected. Then, we will install an additional drive(s) and, finally, add the drive to a storage pool within Synology DSM.

In a previous article I showed how easy it is to get started with a new Synology NAS, including drive installation. Synology DiskStation DS1520+ Overview and DSM Initial Setup Guide.

When you get a Synology NAS for the first time, it is not required to immediately populate all the drive slots. You can start out with one or two drives (depending on your model) and then expand the capacity over time by installing additional drives. For instance, I have a Synology DS1520+, which has five drive bays available. But right now, I only have two 4TB Seagate IronWolf drives installed. These drives are configured with RAID SHR in a single storage pool. Now, I got an additional 4TB drive that I will add to the NAS to expand the storage pool's capacity.

With this configuration, you should expect not only additional capacity but also a slight performance gain. Of course, this is based on the layout of the current pool and your NAS system.

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1. Considerations Before Expanding a Storage Pool

1.1. Considerations 

  1. Needless to say, you need to make sure you have a free drive slot on the NAS itself.
  2. Drives can be added to storage pools in the following RAID configurations: A Synology Hybrid RAID (SHR) consisting of at least 2 drives, JBOD, RAID 5, RAID 6, or RAID F1.
  3. You need a drive of the same size or larger than the smallest drive in your current pool. If you use regular RAID (RAID 5, RAID 6, or RAID F1), you need to consider the smallest drive size. However, if you use SHR, you can use larger-capacity drives to get additional storage by adding these. 
  4. Use the Synology RAID calculator to make sure what capacity you will get in your storage pool.
  5. Depending on your drives, data, and the used/available capacity of your storage pool, this process can take a very long time. Take this into account and be patient.
  6. Backup your data if you consider it necessary. 

1.2. Important Recommendations

If you have an expansion unit, do not create or expand a RAID (storage) pool across your Synology and the expansion unit. So, if you have the idea, forget about it. Imagine if your eSATA port fails or the eSATA connector between the two appliances gets accidentally unplugged. The drives' connection will fail, and you might lose the entire storage pool along with its volumes.

The recommendation is to create two different storage pools, one per appliance (NAS and expansion unit), and then create separate volumes in each of these devices/pools. For instance, the NAS I am using is the DS1520+, with two eSATA ports, two connect up to two DX517. If you have three appliances/devices (NAS + two expansion units), you should create three different volumes within three individual storage pools.

1.3. Monitor the Condition of the Current Drives

Log in to your Synology system (DSM). Go to Main Menu > Storage Manager. From here, make sure the system, volumes, and storage pools are marked as Healthy.

synology storage manager-overview

Then, move to the HDD/SSD page and confirm that your drives' state is Healthy.

synology storage HDD SSD healthy check

Each drive is color-coded to indicate its overall status:

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  • Green: The drive is in good condition, or its warning status has been suppressed or disabled.
  • Orange: The drive is in abnormal status. Please pay attention to the drive's health status and allocation status.
  • Red: Critical issues have been detected on the drive. Please replace the drive immediately.
  • Blue: The drive is processing one or multiple tasks.
  • Gray: The drive is disabled.

Note: I have been doing some pre-tests before configuring my NAS. So currently, I just have a couple of small files in it. 

1.4. Run a S.M.A.R.T. and IronWolf Test on your Drives

You can run your S.M.A.R.T. test on your drives. Also, IronWolf test if you are using Seagate drives. 

"S.M.A.R.T. (Self-Monitoring, Analysis and Reporting Technology) is a monitoring system included in computer hard disk drives (HDDs), solid-state drives (SSDs), and eMMC drives. Its primary function is to detect and report various indicators of drive reliability with the intent of anticipating imminent hardware failures."

Take into account that there are various approaches to test your drives. When you run a S.M.A.R.T. test, you can do it either per individual drive or in all your drives at the same time. For the latter, the test can be scheduled to run automatically on drives.

On the HDD/SSD page, go to the Test Scheduler tab and click on Create.

synology SMART test

The new window, Create Task, will be promoted. Here, on the General tab, select the type of task you want to create. In my case, I choose All, to include both S.M.A.R.T. and IronWolf tests. Select the options below according to your needs. If you keep scrolling down, you'll see the options for the IronWolf Health test.

synology smart test

On the Schedule tab, you can select a specific date to run the test. Click OK.

synology schedule smart test

After the Schedule is set, you can actually run it immediately. Select the newly created task > Run > Yes

synology run a smart test

Notice that not all S.M.A.R.T. features are supported on SAS drives or NVMe SSDs. Also, the IronWolf Health test is supported only on specific Seagate drives. 

From the HDD/SDD page, Go to HDD/SSD > Health Info > History. Here, you can view and export the health diagnosis results and view the history of the significant S.M.A.R.T. attributes.

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synology view smart test results

Note: As I mentioned, I have been doing some pre-tests, and I just have a couple of small files in it. If your drives are almost full, expect a considerable time (maybe days) to carry on this operation.

2. Install New Drive(s) in your NAS

This is the easy part. In a previous article, I showed how easy it is to get started with a new Synology NAS, including drive installation. 

Synology DiskStation DS1520+ Overview and DSM Initial Setup Guide.

 If your Synology NAS supports hot-swapping, you can go ahead and install your drives now. If not, you must power off your Synology NAS first. Then insert a new drive into an empty drive slot.

3. Add a Drive to a Storage Pool within Synology DSM

Go to Main Menu > Storage Manager > Storage Pool. Under the Storage Pool tab, Select the storage pool you want to expand (I only have one, in my case). Click Add Drive from the Action drop-down menu. Notice the Add Drive option is only available once you installed the new HDD. 

synology add drive storage pool

Select the drive you want to add from the list—only one in my case. Click Next and OK to the warning message. Notice that only drives that meet the type and capacity requirements will be listed, also that the data in all newly added drives will be erased. 

synology choose drives expand pool

Confirm the setting and click Apply. You'd have to wait for a while until Synology DSM completes this process. This time will depend on how much data you have in your current pool and how large your drives are. As a matter of fact, after 3.5 hours, only 15% of the expansion operation has been completed, in my case

synology storage pool expanding process

4. Expand the volume size (Optional)

Once a storage pool contains sufficient capacity, the size of its corresponding volume can be expanded either automatically or manually, depending on the storage pool type.

Single-volume storage pool: For a storage pool that supports a single volume, the volume size will be expanded automatically once the storage pool capacity has been expanded.

Multiple-volume storage pool: For a storage pool that supports multiple volumes, the volume size can be expanded manually once the storage pool contains sufficient capacity. 

Instead of using either option, I will create an additional volume for a variety of data. The decision is totally up to you.


If there are empty drive slots on your Synology NAS, you can install additional drives and add them to an existing storage pool. There are various considerations and steps to follow to properly expand a storage pool for a Synology NAS. This guide covered all the essential requirements to expand an existing storage pool by installing additional drives.

The process is straightforward, possible to Synology DSM. I expanded a pool containing two HDDs with a third one. During the process and following all the recommendations, no issues were presented. 



Synology RAID calculator

Synology DSM 6.2 User Guide

Juan Mulford
Juan Mulford
I have been active in IT for over fourteen years now. I am a solutions architect, working with storage, virtualization, and VDI solutions. For the past ten years, I have been living and working in Taiwan.

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