Using Volumes On Synology NAS

You can create separate Volumes on your Synology DiskStation. What are the benefits, the do’s and don’ts? In this post I collect the reasons to consider to create multiple Volumes or Storage Pools.

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Using Volumes On Synology NAS

When you install a Synology NAS for the first time or ignore custom options, the process will combine all disks into a single Storage Pool and use that entire pool for a single Volume. However, there are other options where you create more Volumes and optionally separate Storage Pools as well.

What is the purpose of having multiple Volumes on your Synology NAS? Before we dig into this, let’s determine a few facts on how a DiskStation handles Volumes.

Disks, storage pool, and volume

Your DiskStation combines disks into one or more Storage Pools. On each Storage Pool, you create one or more Volumes.

{illustration of 4 disks and different pools and volumes}

The RAID or SHR level of the Storage Pool determines the kind of redundancy of that pool and as a result for every Volume on that pool.

On a Storage Pool, you create one or more Volumes. You can have multiple Volumes on the same Storage Pool or create separate Storage Pools with their own Volume.

A Volume is limited in size. Older and some recent base models have a 16TB limit. For other models, the limit is 108TB up to 200TB.

A Volume has a file system. On a Synology DiskStation, you can choose between the basic EXT4 and the more advanced Btrfs file system.

Note that some DiskStaton models only support EXT4 as a file system.


There are (at least) three features of DSM related to Volumes. DSM or DiskStation Manager is the operating system of your Synology DiskStation.

When you install a package, create a shared folder, or enable the user home service, you can select a Volume if there is more than one. Note that there are a few packages that do not offer Volume selection.

File system

A Volume is formatted with a file system. Most Synology NAS models let you choose between Btrfs and EXT4. Some – typically basic models – support EXT4 only. The Btrfs file system is more versatile, where EXT4 gives higher performance.


The graph above highlights some of the differences. For example, with the EXT4 file system, a quota is only enforced per Volume, not per Shared Folder, as is the case with Btrfs. As a result, where quotas are concerned, you could be more inclined to create multiple Volumes with the EXT4 file system.

On the other hand, you might create a separate Volume with EXT4 for applications like Surveillance Station or a website.


For NAS models that support an SSD cache, it is good to know that a cache is assigned per Volume.

Let us now look at some decisions you could make when designing Storage Pools and Volumes in a Synology DiskStation.

Separate Types Of Data

You can store different kinds of data on different Volumes for a better overview. You do not necessarily have to create separate Storage Pools for each Volume, but you could.

For example, you have all the user home folders on one Volume and all Shared Folders on the other. Or you might install services and applications from Synology packages on a specific Volume separated from other data.

When you backup other computers to your Synology NAS, you might want to create a separate Volume for that.

Hardware Requirement

Some DiskStation models have the option to extend their capacity with an expansion unit. Synology offers different expansion units like the DX517 and DX1215 desktop models and several rack-mount models.

Best practices for these expansion units tell us to create a Storage Pool separate from the main chassis. In other words, do not combine drives in the DiskStation’s main chassis with drives in the expansion unit into a single Storage Pool. This will degrade performance significantly.

Software Requirement

Some services or applications require a specific file system, like Btrfs. Examples are the Virtual Machine Manager application and Snapshots. Other applications are more suited to the EXT4 file system, like a website.

A file system is a property of a Volume. Note that you can create multiple Volumes on the same Storage Pool.

Different Redundancies

You always have multiple Volumes with different Storage Pools because you have at least one Volume per Storage Pool. You can not span a Volume over different Storage Pools.

You can give each Storage Pool its specific RAID configuration depending on the need for redundancy, storage, or performance characteristics.

Your movie collection, for example, is static and may grow slowly over the years. Assuming you have a backup, redundancy is not a requirement, but storage space is. You can sacrifice redundancy for space and create a separate Storage Pool and Volume for it.

Your data in Shared Folders, on the other hand, is very dynamic, and availability is paramount. A high level of redundancy is mandatory.

Storing your movie collection on a separate Storage Pool, and therefore Volume makes a lot of sense. Note that different data can have different backup schedules. I will mention this below.

Performance Gain

When you separate data over different Storage Pools, you might achieve better performance. For example, while one pool is storing a backup, another pool can serve data to users. The disks will become less of a bottle-neck, assuming you have HDDs, not SSDs.

Talking SSD: an SSD cache is assigned per Volume. You can collect data that benefit from a cache on a single Volume that you assign the cache to, separate from data that do not benefit from a cache.

Maintenance And Backup

When a Volume or Storage Pool fills up, you only need to upgrade the disks for that pool, not the entire disk set in your DiskStation. This makes maintenance easier. When you backup data per Volume, you can backup dynamic data more frequently than other data that is more static.

While talking about an expansion unit with its own Storage Pool, you can use this unit exclusively for one of your backups.

What Do You Think

Do you use multiple volumes in a single NAS? How did you set this up, and what goal was achieved?

When designing your NAS in terms of disks, Storage Pools, and Volumes, I suggest you first make an inventory of the different kinds of data that you like to store on it. Next, you translate that into Volumes and their file system.

With your list of Volumes, you translate that into Storage Pools. You have the option to combine Volumes on a single Storage Pool or divide them over different pools. This obviously depends on the disks you have available.

It may be clear that a DiskStation with 5 bays is more flexible in terms of Volumes and Storage Pools than a 2-bay model.


Paul Steunebrink / Storage Alchemist

2 thoughts on “Using Volumes On Synology NAS”

  1. Thanks Paul. I’ve had a Synology DS415play since ’15, and have it (1 pool) separated into 3 volumes, which I haven’t really used beyond volume 1. Having realized the limitations with that 32 bit machine, and wanting to be able to use docker and some other apps like mail station plus which won’t run on that, I just purchased a DS1520+. I’m trying to figure out how best to organize everything, and am at a loss as to whether I should go with more than 1 volume, or even more than one storage pool . I got 5 WD red plus’s for it (CRMs) in a package deal from B&H Photo, installed them all but 2 were DOA and I sent them back for replacement. Waiting for them now, but the other 3 are in and running SHR1 in 1 pool and 1 volume. When I get the replacement 2, I assume it will allow me to add as new pool and/or a 2nd volume. In looking around a bit on the internet your article seems to offer the most comprehension with regard to pools and volumes.

    1. Hi Sam,
      With regard to adding new drives and the ability to create a new pool, versus adding to an existing pool, I do not have this experience firsthand. What I read is that drives are added automatically to the existing pool but maybe there is an option that users overlook that will allow you to choose a different configuration (I would expect it does).
      Whether or not separate pools and volumes are beneficial to your setup, depends on the kind of data, the static or dynamic nature, performance requirements, file system etc. what I outline in the post. I suggest you write down for yourself what it is that you want to achieve. These requirements translate into the desired configuration.
      Best regards, Paul Steunebrink / Storage Alchemist

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