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This article describes minimum hardware requirements for Storage Spaces Direct. For hardware requirements on Azure Stack HCI, our operating system designed for hyperconverged deployments with a connection to the cloud, see Before you deploy Azure Stack HCI: Determine hardware requirements.

For production, Microsoft recommends purchasing a validated hardware/software solution from our partners, which include deployment tools and procedures. These solutions are designed, assembled, and validated against our reference architecture to ensure compatibility and reliability, so you get up and running quickly. For hardware solutions, visit the Azure Stack HCI solutions website.

 Tip

Want to evaluate Storage Spaces Direct but don't have hardware? Use Hyper-V or Azure virtual machines as described in Using Storage Spaces Direct in guest virtual machine clusters.

Base requirements

Systems, components, devices, and drivers must be certified for the operating system you’re using in the Windows Server Catalog. In addition, we recommend that servers and network adapters have the Software-Defined Data Center (SDDC) Standard and/or Software-Defined Data Center (SDDC) Premium additional qualifications (AQs), as pictured below. There are over 1,000 components with the SDDC AQs.

The fully configured cluster (servers, networking, and storage) must pass all cluster validation tests per the wizard in Failover Cluster Manager or with the Test-Cluster cmdlet in PowerShell.

In addition, the following requirements apply:

Servers

  • Minimum of 2 servers, maximum of 16 servers
  • Recommended that all servers be the same manufacturer and model

CPU

  • Intel Nehalem or later compatible processor; or
  • AMD EPYC or later compatible processor

Memory

  • Memory for Windows Server, VMs, and other apps or workloads; plus
  • 4 GB of RAM per terabyte (TB) of cache drive capacity on each server, for Storage Spaces Direct metadata

Boot

  • Any boot device supported by Windows Server, which now includes SATADOM
  • RAID 1 mirror is not required, but is supported for boot
  • Recommended: 200 GB minimum size

Networking

Storage Spaces Direct requires a reliable high bandwidth, low latency network connection between each node.

Minimum interconnect for small scale 2-3 node

  • 10 Gbps network interface card (NIC), or faster
  • Two or more network connections from each node recommended for redundancy and performance

Recommended interconnect for high performance, at scale, or deployments of 4+

  • NICs that are remote-direct memory access (RDMA) capable, iWARP (recommended) or RoCE
  • Two or more network connections from each node recommended for redundancy and performance
  • 25 Gbps NIC or faster

Switched or switchless node interconnects

  • Switched: Network switches must be properly configured to handle the bandwidth and networking type. If using RDMA that implements the RoCE protocol, network device and switch configuration is even more important.
  • Switchless: Nodes can be interconnected using direct connections, avoiding using a switch. It's required that every node has a direct connection with every other node of the cluster.

Drives

Storage Spaces Direct works with direct-attached SATA, SAS, NVMe, or persistent memory (PMem) drives that are physically attached to just one server each. For more help choosing drives, see the Choosing drives and Understand and deploy persistent memory articles.

  • SATA, SAS, persistent memory, and NVMe (M.2, U.2, and Add-In-Card) drives are all supported
  • 512n, 512e, and 4K native drives are all supported
  • Solid-state drives must provide power-loss protection
  • Same number and types of drives in every server – see Drive symmetry considerations
  • Cache devices must be 32 GB or larger
  • Persistent memory devices are used in block storage mode
  • When using persistent memory devices as cache devices, you must use NVMe or SSD capacity devices (you can't use HDDs)
  • If you're using HDDs to provide storage capacity, you must use storage bus caching. Storage bus caching isn't required when using all-flash deployments
  • NVMe driver is the Microsoft-provided one included in Windows (stornvme.sys)
  • Recommended: Number of capacity drives is a whole multiple of the number of cache drives
  • Recommended: Cache drives should have high write endurance: at least 3 drive-writes-per-day (DWPD) or at least 4 terabytes written (TBW) per day – see Understanding drive writes per day (DWPD), terabytes written (TBW), and the minimum recommended for Storage Spaces Direct

 Note

When using all flash drives for storage capacity, the benefits of storage pool caching will be limited. Learn more about the storage pool cache.

Here's how drives can be connected for Storage Spaces Direct:

  • Direct-attached SATA drives
  • Direct-attached NVMe drives
  • SAS host-bus adapter (HBA) with SAS drives
  • SAS host-bus adapter (HBA) with SATA drives
  • NOT SUPPORTED: RAID controller cards or SAN (Fibre Channel, iSCSI, FCoE) storage. Host-bus adapter (HBA) cards must implement simple pass-through mode for any storage devices used for Storage Spaces Direct.

Drives can be internal to the server, or in an external enclosure that is connected to just one server. SCSI Enclosure Services (SES) is required for slot mapping and identification. Each external enclosure must present a unique identifier (Unique ID).

  • Drives internal to the server
  • Drives in an external enclosure ("JBOD") connected to one server
  • NOT SUPPORTED: Shared SAS enclosures connected to multiple servers or any form of multi-path IO (MPIO) where drives are accessible by multiple paths.

Minimum number of drives (excludes boot drive)

The minimum number of capacity drives you require varies with your deployment scenario. If you're planning to use the storage pool cache, there must be at least 2 cache devices per server.

You can deploy Storage Spaces Direct on a cluster of physical servers or on virtual machine (VM) guest clusters. You can configure your Storage Spaces Direct design for performance, capacity, or balanced scenarios based on the selection of physical or virtual storage devices. Virtualized deployments take advantage of the private or public cloud's underlying storage performance and resilience. Storage Spaces Direct deployed on VM guest clusters allows you to use high availability solutions within virtual environment.

The following sections describe the minimum drive requirements for physical and virtual deployments.

Physical deployments

This table shows the minimum number of capacity drives by type for hardware deployments such as Azure Stack HCI version 21H2 or later, and Windows Server.

Drive type present (capacity only)Minimum drives required (Windows Server)Minimum drives required (Azure Stack HCI)
All persistent memory (same model) 4 persistent memory 2 persistent memory
All NVMe (same model) 4 NVMe 2 NVMe
All SSD (same model) 4 SSD 2 SSD

If you're using the storage pool cache, there must be at least 2 more drives configured for the cache. The table shows the minimum numbers of drives required for both Windows Server and Azure Stack HCI deployments using 2 or more nodes.

Drive type presentMinimum drives required
Persistent memory + NVMe or SSD 2 persistent memory + 4 NVMe or SSD
NVMe + SSD 2 NVMe + 4 SSD
NVMe + HDD 2 NVMe + 4 HDD
SSD + HDD 2 SSD + 4 HDD

 Important

The storage pool cache cannot be used with Azure Stack HCI in a single node deployment.

Virtual deployment

This table shows the minimum number of drives by type for virtual deployments such as Windows Server guest VMs or Windows Server Azure Edition.

Drive type present (capacity only)Minimum drives required
Virtual Hard Disk 2

 Tip

To boost the performance for guest VMs when running on Azure Stack HCI or Windows Server, consider using the CSV in-memory read cache to cache unbuffered read operations.

If you're using Storage Spaces Direct in a virtual environment, you must consider:

  • Virtual disks aren't susceptible to failures like physical drives are, however you're dependent on the performance and reliability of the public or private cloud
  • It's recommended to use a single tier of low latency / high performance storage
  • Virtual disks must be used for capacity only

Learn more about deploying Storage Spaces Direct using virtual machines and virtualized storage.

Maximum capacity

MaximumsWindows Server 2019 or laterWindows Server 2016
Raw capacity per server 400 TB 100 TB
Pool capacity 4 PB (4,000 TB) 1 PB
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This topic describes how to add servers or drives to Storage Spaces Direct.

Adding servers

Adding servers, often called scaling out, adds storage capacity and can improve storage performance and unlock better storage efficiency. If your deployment is hyper-converged, adding servers also provides more compute resources for your workload.

Typical deployments are simple to scale out by adding servers. There are just two steps:

  1. Run the cluster validation wizard using the Failover Cluster snap-in or with the Test-Cluster cmdlet in PowerShell (run as Administrator). Include the new server <NewNode> you wish to add. 
    Test-Cluster -Node <Node>, <Node>, <Node>, <NewNode> -Include "Storage Spaces Direct", Inventory, Network, "System Configuration"
    This confirms that the new server is running Windows Server 2016 Datacenter Edition, has joined the same Active Directory Domain Services domain as the existing servers, has all the required roles and features, and has networking properly configured.
  2.  Important
  3. If you are re-using drives that contain old data or metadata you no longer need, clear them using Disk Management or the Reset-PhysicalDisk cmdlet. If old data or metadata is detected, the drives aren't pooled.
  4. PowerShellCopy
  5. Run the following cmdlet on the cluster to finish adding the server:
Copy 
Add-ClusterNode -Name NewNode

 Note

Automatic pooling depends on you having only one pool. If you've circumvented the standard configuration to create multiple pools, you will need to add new drives to your preferred pool yourself using Add-PhysicalDisk.

From 2 to 3 servers: unlocking three-way mirroring

With two servers, you can only create two-way mirrored volumes (compare with distributed RAID-1). With three servers, you can create three-way mirrored volumes for better fault tolerance. We recommend using three-way mirroring whenever possible.

Two-way mirrored volumes cannot be upgraded in-place to three-way mirroring. Instead, you can create a new volume and migrate (copy, such as by using Storage Replica) your data to it, and then remove the old volume.

To begin creating three-way mirrored volumes, you have several good options. You can use whichever you prefer.

Option 1

Specify PhysicalDiskRedundancy = 2 on each new volume upon creation.

PowerShellCopy 
New-Volume -FriendlyName <Name> -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -Size <Size> -PhysicalDiskRedundancy 2

Option 2

Instead, you can set PhysicalDiskRedundancyDefault = 2 on the pool's ResiliencySetting object named Mirror. Then, any new mirrored volumes will automatically use three-way mirroring even if you don't specify it.

PowerShellCopy 
Get-StoragePool S2D* | Get-ResiliencySetting -Name Mirror | Set-ResiliencySetting -PhysicalDiskRedundancyDefault 2

New-Volume -FriendlyName <Name> -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -Size <Size>

Option 3

Set PhysicalDiskRedundancy = 2 on the StorageTier template called Capacity, and then create volumes by referencing the tier.

PowerShellCopy 
Set-StorageTier -FriendlyName Capacity -PhysicalDiskRedundancy 2

New-Volume -FriendlyName <Name> -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -StorageTierFriendlyNames Capacity -StorageTierSizes <Size>

From 3 to 4 servers: unlocking dual parity

With four servers, you can use dual parity, also commonly called erasure coding (compare to distributed RAID-6). This provides the same fault tolerance as three-way mirroring, but with better storage efficiency. To learn more, see Fault tolerance and storage efficiency.

If you're coming from a smaller deployment, you have several good options to begin creating dual parity volumes. You can use whichever you prefer.

Option 1

Specify PhysicalDiskRedundancy = 2 and ResiliencySettingName = Parity on each new volume upon creation.

PowerShellCopy 
New-Volume -FriendlyName <Name> -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -Size <Size> -PhysicalDiskRedundancy 2 -ResiliencySettingName Parity

Option 2

Set PhysicalDiskRedundancy = 2 on the pool's ResiliencySetting object named Parity. Then, any new parity volumes will automatically use dual parity even if you don't specify it

PowerShellCopy 
Get-StoragePool S2D* | Get-ResiliencySetting -Name Parity | Set-ResiliencySetting -PhysicalDiskRedundancyDefault 2

New-Volume -FriendlyName <Name> -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -Size <Size> -ResiliencySettingName Parity

With four servers, you can also begin using mirror-accelerated parity, where an individual volume is part mirror and part parity.

For this, you will need to update your StorageTier templates to have both Performance and Capacity tiers, as they would be created if you had first run Enable-ClusterS2D at four servers. Specifically, both tiers should have the MediaType of your capacity devices (such as SSD or HDD) and PhysicalDiskRedundancy = 2. The Performance tier should be ResiliencySettingName = Mirror, and the Capacity tier should be ResiliencySettingName = Parity.

Option 3

You may find it easiest to simply remove the existing tier template and create the two new ones. This will not affect any pre-existing volumes which were created by referring the tier template: it's just a template.

PowerShellCopy 
Remove-StorageTier -FriendlyName Capacity

New-StorageTier -StoragePoolFriendlyName S2D* -MediaType HDD -PhysicalDiskRedundancy 2 -ResiliencySettingName Mirror -FriendlyName Performance
New-StorageTier -StoragePoolFriendlyName S2D* -MediaType HDD -PhysicalDiskRedundancy 2 -ResiliencySettingName Parity -FriendlyName Capacity

That's it! You are now ready to create mirror-accelerated parity volumes by referencing these tier templates.

Example

PowerShellCopy 
New-Volume -FriendlyName "Sir-Mix-A-Lot" -FileSystem CSVFS_ReFS -StoragePoolFriendlyName S2D* -StorageTierFriendlyNames Performance, Capacity -StorageTierSizes <Size, Size>

Beyond 4 servers: greater parity efficiency

As you scale beyond four servers, new volumes can benefit from ever-greater parity encoding efficiency. For example, between six and seven servers, efficiency improves from 50.0% to 66.7% as it becomes possible to use Reed-Solomon 4+2 (rather than 2+2). There are no steps you need to take to begin enjoying this new efficiency; the best possible encoding is determined automatically each time you create a volume.

However, any pre-existing volumes will not be "converted" to the new, wider encoding. One good reason is that to do so would require a massive calculation affecting literally every single bit in the entire deployment. If you would like pre-existing data to become encoded at the higher efficiency, you can migrate it to new volume(s).

For more details, see Fault tolerance and storage efficiency.

Adding servers when using chassis or rack fault tolerance

If your deployment uses chassis or rack fault tolerance, you must specify the chassis or rack of new servers before adding them to the cluster. This tells Storage Spaces Direct how best to distribute data to maximize fault tolerance.

  1. Create a temporary fault domain for the node by opening an elevated PowerShell session and then using the following command, where <NewNode> is the name of the new cluster node: 
    New-ClusterFaultDomain -Type Node -Name <NewNode>
  2. PowerShellCopy
  3. Move this temporary fault-domain into the chassis or rack where the new server is located in the real world, as specified by <ParentName>: 
    Set-ClusterFaultDomain -Name <NewNode> -Parent <ParentName>
    For more information, see Fault domain awareness in Windows Server 2016.
  4. PowerShellCopy
  5. Add the server to the cluster as described in Adding servers. When the new server joins the cluster, it's automatically associated (using its name) with the placeholder fault domain.

Adding drives

Adding drives, also known as scaling up, adds storage capacity and can improve performance. If you have available slots, you can add drives to each server to expand your storage capacity without adding servers. You can add cache drives or capacity drives independently at any time.

 Important

We strongly recommend that all servers have identical storage configurations.

To scale up, connect the drives and verify that Windows discovers them. They should appear in the output of the Get-PhysicalDisk cmdlet in PowerShell with their CanPool property set to True. If they show as CanPool = False, you can see why by checking their CannotPoolReason property.

PowerShellCopy 
Get-PhysicalDisk | Select SerialNumber, CanPool, CannotPoolReason

Within a short time, eligible drives will automatically be claimed by Storage Spaces Direct, added to the storage pool, and volumes will automatically be redistributed evenly across all the drives. At this point, you're finished and ready to extend your volumes or create new ones.

If the drives don't appear, manually scan for hardware changes. This can be done using Device Manager, under the Action menu. If they contain old data or metadata, consider reformatting them. This can be done using Disk Management or with the Reset-PhysicalDisk cmdlet.

 Note

Automatic pooling depends on you having only one pool. If you've circumvented the standard configuration to create multiple pools, you will need to add new drives to your preferred pool yourself using Add-PhysicalDisk.

Optimizing drive usage after adding drives or servers

Over time, as drives are added or removed, the distribution of data among the drives in the pool can become uneven. In some cases, this can result in certain drives becoming full while other drives in pool have much lower consumption.

To help keep drive allocation even across the pool, Storage Spaces Direct automatically optimizes drive usage after you add drives or servers to the pool (this is a manual process for Storage Spaces systems that use Shared SAS enclosures). Optimization starts 15 minutes after you add a new drive to the pool. Pool optimization runs as a low-priority background operation, so it can take hours or days to complete, especially if you're using large hard drives.

Optimization uses two jobs - one called Optimize and one called Rebalance - and you can monitor their progress with the following command:

PowerShellCopy 
Get-StorageJob

You can manually optimize a storage pool with the Optimize-StoragePool cmdlet. Here's an example:

PowerShellCopy 
Get-StoragePool <PoolName> | Optimize-StoragePool
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Below is a step-by-step guide on how to add a third node to an existing 2-node Storage Spaces Direct (S2D) cluster with the production workload still running.

 

1.) Ensure that the cluster is configured with a witness.

2.) Pause/Drain a node in the cluster.

3.) Place the paused node's drives into a storage maintenance mode.

Get-StorageFaultDomain -type StorageScaleUnit | Where-Object {$_.FriendlyName -eq “<Node Name>”} | Enable-StorageMaintenanceMode 

4.) Physically add the 3rd node into the 2-node cluster configuration by cabling the three servers like the image below:

DataON 2U Platforms:

DataON 1U Platform:

5.) Make sure the node that is being added to the cluster has the same firmware and drivers installed as the two servers in the existing 2-node cluster. Also install the necessary Windows features and configure the network correctly. Before adding the third node to the cluster, run a cluster validation.

 

$S1 = "Node1"

$S2 = "Node2"

$S3 = "Node3"

 

$nodes = ($S1,$S2,$S3)

 

Test-Cluster -node $nodes -Include "Storage Spaces Direct",Inventory,Network, "System Configuration" -ReportName C:\Windows\cluster\Reports\report

 

6.) With a clean validation report, proceed to add the third node into the S2D cluster.

<<Add-ClusterNode -Name ‘NewNodeName’ >>

7.) Disable the storage maintenance mode on the drives of the paused node; Resume the node to the cluster.

Get-StorageFaultDomain -type StorageScaleUnit | Where-Object {$_.FriendlyName -eq “<Node Name>”} | Disable-StorageMaintenanceMode 

8.) By adding a third node to the S2D cluster, 3-way-mirror resiliency is unlocked; Run the following command to configure this setting on the existing storage pool.

<< Get-StoragePool S2D* | Get-ResiliencySetting -Name Mirror | Set-ResiliencySetting -PhysicalDiskRedundancyDefault 2>>

9.) Allow S2D optimization job to complete as well as any other storage jobs to finish before creating a new 3-way-mirror virtual disk/CSV.

10.) With the increased capacity from joining the third node to the cluster, you may now create a new volume (3-way-mirror).

 

NOTE: The virtual disks that were previously created will remain as 2-way-mirror resiliency.

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Introduction

The value of business data grows to the extent that companies simply cannot ignore the importance of a safe data storage. Modern technologies offer a variety of methods how to warrant a highly-available and fault-tolerant storage. One of the techniques includes synchronous mirroring – an approach when a source storage has an exact replica (one or more). At the same time, the data is considered written only when the primary storage receives a signal that all secondary copies have been created. This document suggests taking a look at two-way and three-way synchronous mirroring to better understand the benefits each of them has behind.

Cost-efficiency

2-way synchronous mirroring

This configuration requires storage redundancy on the nodes. The use of RAID10* is recommended. 2-node HA ensures the synchronous mirroring of data between two storage nodes. Taking into account that each storage node has only 50% of usable capacity with RAID10, synchronous mirroring makes the further dividing of those 50% by half resulting in the underutilization of storage capacity – only 25% is used.

* RAID10 use is recommended for a HDD setup. In case of RAID5 use in a HDD setup, there arises the risk of disk failure while rebuilding RAID5. RAID6 in a HDD setup gives low write performance. At the same time, RAID5 and RAID6 configurations can be used for SSD setups due to a high tolerance to physical failures and faster performance of the latter.


With 2-way synchronous mirroring, usable capacity is 25% – ¼ of storage space

3-way synchronous mirroring

Non-redundant RAID0 configuration provides the highest level of performance, therefore, RAID0 can be used for performance. Synchronous mirroring between 3 storage nodes with RAID0 configured on each, results in 33% usable capacity and thus provides a higher level of storage utilization compared to 2-way synchronous mirroring.
While it looks like this configuration does not require storage redundancy on nodes (since 3-way synchronous mirroring already ensures the required level of data protection), you should evaluate the potential risks of disks failing and potential data loss probability (if disks failed on all 3 nodes). Assuming the above, please make sure that the data is protected by backup applications according to the 3-2-1 backup rule.

With 3-way synchronous mirroring, usable capacity is 33% – 1/3 of storage space

As a result, 3-way synchronous mirroring increases the storage utilization rate. The cost-efficiency of this configuration differs depending on the medium type – spindle or flash. The difference is shown on the charts below.

Increased reliability

2-way synchronous mirroring

2-way synchronous mirroring provides 99.99% uptime. The outage of one storage node results in a single point of failure and immediately brings the system to a degraded performance mode. Cache is flushed and turned from write-back to write-through mode on the running node. A number of MPIO paths is reduced twofold because one node is down. Consequently, the storage performance falls.

With 2-way synchronous mirroring, there is a risk of downtime

3-way synchronous mirroring

3-way synchronous mirroring provides 99.9999% uptime. No single point of failure occurs when one node of a 3-node storage cluster goes down. In such a situation, storage performance falls by up to 33% because the system loses 1/3 of the MPIO paths. Performance-critical applications usually can continue running in an ordinary way. The 3-node HA configuration tolerates a double fault and retains the availability of service.

With 3-way synchronous mirroring, constant system uptime is ensured

Higher performance

Higher storage performance is influenced by a number of factors, which include I/O policy, RAID level and cache policy. The effect of these factors is given below:

MPIO paths

2-way synchronous mirroring

With Round Robin/List Queue Depth policy used, I/Os are processed up to two times faster comparing to a single-node configuration.

3-way synchronous mirroring

Owing to the Round Robin/List Queue Depth policy, the I/Os throughput rises by a factor of 3 compared to single-node storage.

As a result, performance is increased by up to 50% compared to a 2-node configuration.

RAID10 vs RAID0

2-way synchronous mirroring

This configuration strongly requires extra redundancy for data protection on the storage nodes themselves. This redundancy can be provided through the use of RAID. RAID10* is recommended for a HDD setup as it ensures mirroring between the disk stripes and makes fast reads and writes. However, storage utilization is considerably low because the same data is mirrored and stored on two stripes of RAID.

* Use of RAID5, RAID6 for a HDD setup is possible but not recommended because of the high probability of a disk failure while rebuilding RAID5, and the low write performance of RAID6. At the same time, RAID5 and RAID6 configurations can be used for SSD setups due to a high tolerance to physical failures and faster performance of the latter.

3-way synchronous mirroring

RAID0 can be used for performance. Both reads and writes are faster here as the system reads the data from all disks simultaneously. With RAID0 you should evaluate the potential risks of disks failing and potential data loss probability (if disks failed on all 3 nodes).

Cache policy

2-way synchronous mirroring

If one node fails, the cache is flushed and turned from write-back to write-through mode and the system immediately switches to a degraded performance mode on reads.

With 2-way synchronous mirroring, cache is flushed and turned to write-through mode causing critical performance degradation

3-way synchronous mirroring

If one node goes down, the system downgrades from a 3 to 2-node cluster and continuous operation with minimal performance degradation (about 33%) due to the absence of one node and because a number of MPIO paths is reduced.

With 3-way synchronous mirroring, cache policy remains write-back that results in minor performance degradation

Important note: Even the highest possible level of redundancy and reliability does not ensure 100% protection against data loss, e.g. due to malicious actions or disaster. So, nothing compares to a good old backup that substantially increases the chances your data is in place.

Conclusion

With synchronous mirroring admins can decide on either two-way mirroring – to ensure basic data protection and high availability, or three-way mirroring – to increase overall system reliability and to also “play games with” cost-efficiency and performance.

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