Frequently Asked Question

Overview

Synology Hybrid RAID (SHR) is an automated RAID management system from Synology, designed to make storage volume deployment quick and easy. If you don't know much about RAID, SHR is recommended to set up the storage volume on your Synology NAS.
You will learn different types of SHR and their advantages/disadvantages over classic single disk/RAID setups. In the end, you will be able to choose a type of RAID or SHR for the best interest of your storage volume. This article assumes that as the admin of your Synology NAS, you are also an experienced network administrator with a firm grasp of RAID management.

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1. What is Synology Hybrid RAID (SHR)?

SHR is an automated RAID management system that makes storage volume deployment easier than traditional RAID systems. SHR will allow users to handle RAID management, expand storage, and maximize storage capability even if they do not have a fine grasp of various RAID levels. SHR allows for 1-disk or 2-disk worth of redundancy - meaning the SHR volume can suffer up to two disks lost, and the data volume will still be available for use. Note that a RAID volume (either Classic RAID or SHR) is not a backup system.
Note: RAID (Redundant Array of Independent Disks) is a storage technology that combines multiple disk drive components into a logical unit.

Is SHR required?

No, it is not necessary to use SHR. SHR is based on a Linux RAID management system, and is completely optional to use. SHR not only benefits expert users of traditional RAID systems but also novice users with little technical background when they seek storage data protection. However, SHR is not supported across all Synology NAS models. To know the SHR-unsupportive models, please refer to this article.
For expert users, Classic RAID-levels are recommended if they prefer to manually manage the RAID system. The following manual RAID levels may be available on your Synology NAS:

1. Basic
2. JBOD
3. RAID 0
4. RAID 1
5. RAID 5
6. RAID 6
7. RAID 10

How does SHR maximize storage?

The graph above shows Classic RAID creates the storage volume based upon the smallest disk within the array. If a Classic RAID array is created with a 500 GB drive, all the other drives within the array can only contribute 500 GB for storage each, therefore creating a 5 x 500 GB RAID volume and wasting the other unused 4.5 TB.
Unlike Classic RAID, SHR divides each drive volume into smaller chunks and creates additional redundant storage. By using SHR, you can use the unavailable 4.5 TB volume as smaller usable chunks, therefore maximizing storage capacity of each drive.

Expanding with larger disks with SHR

SHR also outstrips Classic RAID when users are expanding the storage.
As the graph above shows, Classic RAID does not allow the upgraded storage for use until all the drives are upgraded.
Unlike Classic RAID, SHR makes the newly upgraded storage readily available for use. If the drives are replaced with larger ones, the upgraded storage can be used as soon as two of the disks are upgraded to form a redundant storage array.
This quick-for-use feature of SHR allows users to meet the rising needs of frequently upgrading large disks arrays (e.g., a 10-bay volume) while making the data accessible on demand. In addition, as a financially viable approach, SHR helps users achieve maximum storage capacity without purchasing an entire set of drives.

Synology Hybrid RAID with 2-Disk Redundancy

2-disk redundant version of the SHR is available since DSM 3.1. To use 2-disk redundant SHR, you will need 4 drives in minimum to create the volume. If you want to expand a 2-disk redundant SHR volume, the new storage will be available right after you add four drives into the SHR volume or expand four of the existing drives in it.
Note: It is impossible to convert 1-disk redundant SHR to 2-disk redundant SHR.

2. Frequently Asked Questions

Can I expand an SHR volume with larger drives, such as 1TB to 3TB?

Yes, you can expand an SHR volume by changing the drives one at a time, and allow the DiskStation Manager to repair the volume. As soon as enough redundant storage is available, the SHR volume will expand the usable storage capacity.

Can I expand an SHR volume with additional drives, such as 5 x 1TB to 15 x 1TB drives?

Yes, you can expand an SHR volume by adding additional drives to the existing array, especially for those who want to expand their storage due to their budget or storage needs.
Note that if you expand an SHR volume with more drives, your Synology NAS may require a lot of time to make all the installed drives usable. We suggest you a quick way for expansion: Schedule the time for expansion, and expand the drives when your Synology NAS is in use. After all, expanding the drives is more time-efficient than adding more drives.

Does an already-created SHR volume accept drives of smaller capacity?

Suppose your SHR volume is built on 1TB drives. To replace the old drives or add new ones, you will have to use drives equal or greater than 1TB. A smaller drive (e.g., 500GB) cannot be added to the existing SHR (or Classic RAID) volume. Even if this smaller drive is added, the storage of the smaller drive still cannot be used within the volume.

Can I change the disk fault tolerance of an SHR volume to 1-disk fault tolerance?

Yes. If your single-disk SHR volume goes without disk fault tolerance, you can add one more drive to establish 1-disk fault tolerance, an equivalent to the data redundancy of RAID 1:

1. Install an additional hard drive in your Synology NAS.
2. Go to Storage Manager > Volume > Manage > Expand the volume by adding hard disks.
3. When the new drive is added to the SHR volume, the volume will have 1-disk fault tolerance.