What is SHR? Synology Hybrid RAID Explained

SHR, or Synology Hybrid RAID, is a proprietary automated RAID management system built into Synology's DSM operating system that intelligently allocates storage across drives of different sizes. Something standard RAID configurations cannot do efficiently. It's one of the features that makes Synology NAS devices accessible to home users and small businesses who don't want to think deeply about storage architecture. Whether you're setting up a two-bay DS225+ or a five-bay DS1525+, SHR handles the complexity of RAID layout so you don't have to.

What Problem Does SHR Solve?

To understand why SHR exists, you need to understand the core limitation of standard RAID with mixed drives. In a traditional RAID 1 or RAID 5 setup, all drives are treated as if they're the same size. Specifically, the size of the smallest drive in the array. If you have three drives of 4TB, 6TB, and 8TB in a RAID 5 configuration, the system uses only 4TB from each drive. You lose 10TB of usable capacity from the larger drives entirely.

This is a real-world problem for NAS buyers who expand their storage over time. Most people don't replace all drives at once. They add a larger drive when an old one fills up, or they repurpose drives from an old system. Standard RAID punishes you for this by wasting capacity. SHR solves this by partitioning drives intelligently so that capacity from larger drives is used rather than abandoned.

How SHR Actually Works

Under the hood, SHR uses a Linux mdraid-based architecture combined with LVM (Logical Volume Manager) to manage how drive capacity is allocated. When you add drives of different sizes, SHR breaks each drive into partitions and groups matching-sized partitions into RAID 1 or RAID 5 sub-arrays. Remaining capacity on larger drives is then paired with partitions from other drives to form additional sub-arrays.

In plain terms: SHR treats each drive as a set of blocks and assembles those blocks into protected sub-volumes rather than requiring all drives to be uniform. DSM presents the entire resulting volume to you as a single unified storage pool, so you never need to think about the partitioning logic underneath. From your perspective, you have one pool of protected storage.

This architecture also means SHR storage pools can be expanded non-destructively. You can replace a drive with a larger one, wait for the array to rebuild, and repeat. Gradually increasing your total capacity without reinstalling DSM or losing your data.

SHR vs SHR-2: What's the Difference?

Synology offers two variants of SHR, and the distinction is important when it comes to fault tolerance:

• SHR (sometimes called SHR-1): Protects against a single drive failure. If one drive in your array fails, the pool survives and data remains accessible. Requires a minimum of two drives. This is the standard choice for most home and SMB deployments.
• SHR-2: Protects against simultaneous failure of two drives. Requires a minimum of four drives. SHR-2 behaves similarly to RAID 6 in terms of redundancy but with the same mixed-drive capacity benefits. SHR-2 suits deployments where uptime and data integrity are critical. Think small business file servers or archival NAS units where a second drive failure during a rebuild would be catastrophic.

It's worth being clear about what SHR does not do: it is not a backup. SHR protects against hardware failure. A failed drive. But it does not protect against accidental deletion, ransomware, file corruption, or a NAS unit that is stolen or destroyed. Any serious data strategy needs SHR (or another RAID type) plus an offsite or cloud backup, such as Synology's own Hyper Backup.

SHR vs Standard RAID on Synology NAS

DSM supports both SHR and standard RAID types including RAID 0, RAID 1, RAID 5, RAID 6, and RAID 10. The choice isn't always SHR by default. It depends on your use case and drive configuration.

The practical guidance is straightforward. If you have identical drives. All the same capacity and ideally the same model. Standard RAID 5 or RAID 6 is a valid and slightly more portable choice (because standard RAID arrays can in theory be moved to non-Synology hardware, though this is rarely a real-world concern for home users). If you have drives of different sizes, or expect to add different-sized drives in future, SHR makes more sense and will use your hardware more efficiently.

On two-bay devices like the DS225+ (from $585 at Mwave) or DS725+ (from $869 at Mwave), SHR behaves the same as RAID 1 when both drives are identical. The difference only becomes apparent when you mix drive sizes or expand over time.

Which Synology Models Support SHR?

SHR is available on most consumer and prosumer Synology DiskStation models, but the availability of SHR-2 depends on the number of drive bays. Here's how it maps across currently available Australian models:

Model	Bays	SHR	SHR-2	AU Price From
DS223J	2	Yes	No	$319 (PLE Computers)
DS223	2	Yes	No	$479 (PLE Computers)
DS225+	2	Yes	No	$585 (Mwave)
DS725+	2	Yes	No	$869 (Mwave)
DS423	4	Yes	Yes	$635 (Scorptec)
DS425+	4	Yes	Yes	$819 (Scorptec)
DS925+	4	Yes	Yes	$995 (Scorptec)
DS1525+	5	Yes	Yes	$1,285 (Mwave)
DS1825+	8	Yes	Yes	$1,799 (Scorptec)

SHR-2 requires a minimum of four drives to function, so it's only available on four-bay and larger models. On two-bay units, your redundancy options are SHR (single drive protection) or RAID 1. Both provide the same level of fault tolerance on a two-drive configuration. The DS124 single-bay unit does not support any RAID or SHR, as redundancy requires at least two drives.

Rackmount models including the RS422+, RS822+, and RS1221+ support SHR and SHR-2, though in enterprise-grade deployments administrators often prefer standard RAID for familiarity and consistency with non-Synology infrastructure. If you're building out a rack deployment for a business, it's worth discussing RAID type selection with whoever manages your infrastructure.

SHR and the Drive Compatibility Question

What this means for SHR specifically: on current desktop models like the DS425+, DS925+, and DS1525+, you can create SHR storage pools using standard 3.5-inch NAS drives from Seagate and Western Digital without restriction under DSM 7.3. If you're planning to use M.2 NVMe drives for a storage pool (rather than just cache), you'll need drives on Synology's Hardware Compatibility List. Check it at Synology's website before purchasing.

For the typical home or SMB buyer filling a new NAS with Seagate IronWolf or WD Red drives, this is no longer a practical barrier. But the controversy around these restrictions is worth knowing about. It changed how a significant portion of the NAS community views Synology, and some enthusiast users have moved to QNAP or TrueNAS as a result. For straightforward home backup and file sharing use cases, though, the products themselves remain strong.

Setting Up SHR on a Synology NAS

Creating an SHR storage pool in DSM is straightforward. The process sits inside Storage Manager, which is accessible from the DSM desktop. Here's the general flow:

1. Open Storage Manager from the DSM application menu.
2. Click Storage Pool in the left panel, then click Create.
3. Choose your performance profile. For most users, Better Performance (which uses SHR) is the default recommendation.
4. Select SHR or SHR-2 from the RAID type dropdown. SHR-2 will only appear if you have four or more drives available.
5. Select the drives you want to include. DSM will show you the estimated usable capacity based on your selections.
6. DSM will warn you that all data on the selected drives will be erased. Confirm and proceed.
7. Once the pool is created, create a Volume within it, selecting your file system (Btrfs is recommended for most users, as it supports snapshots and data integrity checking).

The initial RAID synchronisation process runs in the background after creation. You can use the NAS during this time, though performance may be slightly reduced until synchronisation completes. On large drives or arrays, this can take many hours. DSM shows progress in Storage Manager.

This kind of setup experience is exactly what DSM is designed for. Approachable enough that non-IT users can get through it without documentation, but with enough detail for those who want to understand what's happening under the hood.

Expanding an SHR Array Over Time

One of SHR's practical advantages for home users is that it handles storage expansion gracefully. As your data grows and drives fill up, you have two main options for expanding an SHR pool:

• Add a new drive (if empty bays are available): Insert the new drive, go to Storage Manager, select the storage pool, and choose to expand by adding a drive. DSM will incorporate the new drive into the SHR pool, optimising capacity allocation automatically.
• Replace a drive with a larger one: Remove one drive from the array, replace it with a larger drive, and let the array rebuild. Repeat for each drive you want to replace. Once all drives have been replaced with larger units, DSM will offer to expand the volume to use the additional space.

This upgrade path is non-destructive. Your data remains accessible throughout, as long as no additional drives fail during the rebuild window. This is where SHR-2's two-drive tolerance becomes valuable in a business context: if a drive fails during a rebuild while using SHR-1, you have no redundancy until the rebuild completes and a second failure would be catastrophic.

For a home user on a four-bay DS425+ (from $819 at Scorptec or PLE Computers), a common upgrade pattern is to start with two 4TB drives in SHR, then add a 6TB or 8TB drive when more space is needed. SHR will use the additional capacity rather than waste it, which standard RAID 5 would struggle to handle efficiently in this configuration.

SHR and Btrfs vs EXT4

When creating a volume on an SHR pool, DSM asks you to choose a file system. The two options are Btrfs and EXT4. This choice is separate from SHR itself. SHR is the RAID layer, the file system sits on top. But it's worth addressing here since it comes up in every storage pool setup.

Btrfs is recommended for most users. It supports Synology's snapshot functionality (which provides an additional layer of protection against accidental deletion and ransomware), inline data checksumming for integrity verification, and better integration with DSM features. The main trade-off is slightly higher CPU and RAM overhead, which is imperceptible on Plus series and above hardware.

EXT4 is simpler and has lower overhead. It suits very low-powered NAS units like the DS223J or older Realtek-based models, or deployments where snapshots aren't needed and raw performance is the priority. Once a volume is created with EXT4, converting to Btrfs requires deleting and recreating the volume. So the choice matters.

For a DS425+ or DS925+ running Btrfs on an SHR pool, you get a storage layer that is both redundant against drive failure and capable of point-in-time snapshot recovery. This combination is what makes Synology a practical solution for small businesses that need data protection without the complexity of enterprise storage systems.

When Not to Use SHR

SHR is the right choice for most home and SMB users, but it's not universally the best option. There are specific cases where standard RAID types make more sense:

• You're using all identical drives and never plan to mix sizes: If you install four identical 8TB drives in a DS425+ and never intend to use mixed sizes, standard RAID 5 is equally efficient and slightly more portable. The capacity output will be identical to SHR in this scenario.
• Enterprise or IT-managed environments: Rackmount deployments managed by IT administrators often prefer standard RAID for documentation consistency, monitoring tool compatibility, and the ability to conceptually explain the array to auditors and colleagues without introducing Synology-specific terminology.
• You want maximum read performance: RAID 0 (no redundancy) or RAID 10 offer performance advantages in specific workloads. These are valid choices where data can be reproduced from another source and the array serves as high-speed scratch storage.
• You're on a single-bay unit: The DS124 doesn't support any RAID or SHR. Data protection on a single-bay unit relies entirely on backup strategy.

Don't choose SHR because it sounds more sophisticated. Choose it because it matches your actual drive configuration and expansion plans.

Frequently Asked Questions About SHR

Related reading: our NAS buyer's guide, our Synology brand guide, and our NAS RAID guide.

Use our free RAID Calculator to work out usable capacity across RAID levels.

Related reading: our NAS explainer.

Use our free RAID Rebuild Risk Calculator to estimate the probability of data loss during a RAID rebuild.

Is SHR better than RAID 5 on a Synology NAS?

It depends on your drive configuration. If all your drives are identical in size, SHR and RAID 5 produce the same usable capacity. SHR offers no advantage in that scenario, though it's also not a disadvantage. If your drives are different sizes, or you plan to expand with larger drives over time, SHR makes significantly better use of available capacity by allocating storage from mixed-size drives efficiently. For most home and SMB users buying a NAS and populating it over time, SHR is the more practical choice.

Can I switch from SHR to RAID 5 (or vice versa) without losing data?

No. Changing the RAID type of an existing storage pool on Synology DSM requires deleting the storage pool and recreating it, which destroys all data on the pool. This is not unique to Synology. It applies to most RAID implementations. If you want to change RAID types, you need to back up all data first, delete the pool, create a new pool with the desired RAID type, and restore your data. This is why choosing the right RAID type at setup matters. For most home users, SHR is the safer default choice.

How much usable storage will I get from SHR with mixed drives?

DSM shows a capacity estimate during storage pool creation before you commit, so you can check your specific configuration. As a general guide: with two drives of different sizes (say, 4TB and 6TB), SHR gives you 4TB of usable protected storage. Equivalent to RAID 1, with the extra 2TB from the larger drive unused. With three or more drives, SHR becomes more efficient, pairing matched partitions into RAID 5-style sub-arrays and reducing wasted capacity. The benefit over standard RAID grows as you add more mixed-size drives. For an exact figure for your configuration, Synology's RAID calculator on their website provides accurate estimates.

Will SHR work with Seagate IronWolf or WD Red drives on a new Synology NAS?

Yes, for 3.5-inch SATA drives on current desktop Plus series models running DSM 7.3 or later. Synology reversed the drive compatibility restrictions introduced in April 2025 with the DSM 7.3 update in October 2025, restoring full SHR pool creation and drive health monitoring for third-party 3.5-inch HDDs including Seagate IronWolf, WD Red, and similar NAS-grade drives. The restrictions that remain apply to M.2 NVMe drives (which still require Synology HCL-listed models for pool creation) and enterprise rackmount models. For a standard home or SMB setup using 3.5-inch NAS drives, you're not limited to Synology-branded drives.

What happens if a drive fails in an SHR array?

DSM will alert you via email, push notification (via Synology's mobile app), or both. Depending on how you've configured notifications. The storage pool enters a degraded state but remains accessible and online. Your data is still readable and writable. You then replace the failed drive with a new one, and DSM automatically begins a rebuild process, restoring full redundancy. During the rebuild, performance may be reduced, and if a second drive fails during this window (on an SHR-1 array), data loss occurs. This is why keeping a spare drive on hand for larger deployments is good practice, and why SHR-2 suits more critical applications. It tolerates a second failure even during a rebuild.

Does SHR work with SSDs as well as HDDs?

Yes. SHR works with 2.5-inch SATA SSDs and 3.5-inch HDDs for standard storage pools. Following the DSM 7.3 reversal, third-party SATA SSDs are supported on desktop Plus series models. However, M.2 NVMe SSDs used for storage pools (not cache) still require drives from Synology's Hardware Compatibility List. This restriction was not reversed and applies to all current models. If you're planning an all-SSD NAS build using M.2 NVMe drives, check Synology's HCL carefully before purchasing drives to avoid compatibility issues.

Do I need to think about SHR for remote access to my Synology NAS?

SHR is a storage layer concern separate from remote access. However, Australian NBN connections are relevant context here: typical upload speeds on an NBN 100 plan are around 20Mbps, and NBN 50 plans often have even lower upload throughput. This limits how quickly you can access large files stored on your SHR pool remotely. Additionally, some Australian ISPs use CGNAT (Carrier Grade NAT) on NBN connections, which can block direct remote access to your NAS via Synology's QuickConnect or manual port forwarding. If remote access is important to your use case, confirm with your ISP whether you have a dedicated public IP address, or plan to use Synology's QuickConnect relay service as an alternative.