What is Synology Hybrid RAID (SHR)?

Purpose

This article introduces the different SHR types and their advantages/disadvantages over classic RAID types.

Notes:

This article is intended for Synology NAS administrators.
Some Synology NAS models do not support or provide limited support for SHR. For more information, refer to this article.

Contents

What is SHR?
How does SHR maximize storage capacity?
How do I expand the storage capacity of SHR?
Does SHR provide fault tolerance?

Details

What is SHR?

Synology Hybrid RAID (SHR) is Synology's automated RAID management system. SHR allows users to create a flexible storage solution with optimized capacity and performance.¹

SHR is based on a Linux RAID management system and designed to make storage deployment quicker and easier than classic RAID systems. This makes it especially suitable for users who are new to RAID technology.

If you prefer to manually manage your RAID system, we recommend choosing classic RAID on your Synology NAS (e.g., Basic, JBOD, RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10).²

How does SHR maximize storage capacity?

In general, classic RAID bases its storage creation on the smallest drive in the storage pool. As shown in the image below, if the smallest drive in a classic RAID storage pool is 500 GB, all other drives in the storage pool can each only contribute 500 GB. As a result, the storage pool ends up with 2 TB of usable storage and 4.5 TB of wasted storage.

Unlike classic RAID, SHR divides each drive's storage space into smaller chunks and creates additional redundant storage. Using the same example as before, SHR is able to divide the 4.5 TB of unavailable storage into smaller usable chunks and maximize the storage capacity of each drive.

SHR also outperforms classic RAID in terms of storage expansion. As shown in the image below, classic RAID does not allow a storage pool to be expanded until all its drives have been replaced with larger drives.

SHR, on the other hand, allows a storage pool to be expanded as soon as two of the drives are upgraded and can form a redundant storage array.

If you want to expand an SHR with two-drive fault tolerance (i.e., SHR-2), the new storage will be available after you add drives or expand existing ones.

SHR is quick to use and a financially viable approach. It allows you to do the following with ease:

Meet the rising needs of frequently upgrading large drive arrays (e.g., a 10-bay volume) while making the data accessible on demand.
Achieve maximum storage capacity without needing to purchase an entire set of drives.

How do I expand the storage capacity of SHR?

You can expand the storage capacity of an SHR storage pool by either replacing existing drives with ones of a larger size or adding additional drives.

Replace with Larger Drives

Replace the drives one at a time and use Storage Manager to repair the storage pool. Make sure the replacement drives meet the drive requirements. For more information and detailed instructions, refer to the respective help articles for DSM 7 and DSM 6.2.

Add Additional Drives

Insert drives into the empty drive slots and add them to the storage pool. Make sure the additional drives meet the drive requirements. For more information and detailed instructions, refer to the respective help articles for DSM 7 and DSM 6.2.

Does SHR provide fault tolerance?

No Fault Tolerance

A single-drive SHR storage pool comes without fault tolerance.

One-Drive Fault Tolerance

A minimum of two drives is required to create an SHR storage pool that can sustain one drive failure. If you have already created a single-drive SHR storage pool, you can add another drive to increase its number of tolerable drive failures to one—an equivalent to the data redundancy of RAID 1:³

Insert a new drive into an empty drive slot.
Do the following according to your DSM version:
- DSM 7 and above:
  1. Go to Storage Manager > Storage and select the SHR storage pool you want to add drive to.
  2. Click the icon and select Add Drive.
- DSM 6.2 and below:
  1. Go to Storage Manager > Storage Pool and select the SHR storage pool you want to add drive to.
  2. Click Action and select Add Drive.
Select the drive you want to add from the list. Only drives that meet the drive requirements will be listed.
Follow the wizard to finish the process.

Two-Drive Fault Tolerance

A minimum of four drives is required to create an SHR-2 storage pool that can sustain two drive failures. If you have already created an SHR-1 storage pool (one-drive fault tolerance), you can change it to SHR-2 with the Change RAID Type feature.⁴ For more information and detailed instructions, refer to the respective help articles for DSM 7 and DSM 6.2.

Notes:

RAID (classic and SHR) is not a backup solution.
Each Synology NAS model displays what RAID types it supports on its product specifications page.
Adding a drive to a single-drive SHR storage pool only adds fault tolerance but does not increase its storage capacity.
Changing a storage pool from SHR-1 to SHR-2 is available for DSM 6.1 and above.

Further reading

Choose a RAID Type (DSM 7 or DSM 6.2)
The "Add Drive" option cannot be selected. What can I do?

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