Rack-Level Nested Mirror (RLNM) in Storage Spaces Direct on Windows Server 2025
- Avijit Dutta
- Jul 18
- 4 min read
Updated: Jul 23
Article No :: 32
🚀 Rack-Level Nested Mirror (RLNM) in Storage Spaces Direct on Windows Server 2025
✨ Introduction
Storage Spaces Direct (S2D) is a Microsoft technology that enables high-availability, high-performance storage using local disks in a clustered Windows Server environment. With the Windows Server 2025 Insider Preview (Build 26445), Microsoft introduced a game-changing feature: Rack-Level Nested Mirror (RLNM).
Rack-Level Nested Mirror (RLNM) in Storage Spaces Direct on Windows Server 2025 allows data to be mirrored across racks — not just within servers — enhancing redundancy and fault tolerance for enterprise-grade deployments.
⚠️ Disclaimer: This tutorial is designed for educational purposes and lab environments only. While it mirrors production scenarios, please test all configurations in a safe environment before implementing in production.
🔍 What is RLNM?
Rack-Level Nested Mirror (RLNM) enables mirrored data copies to be distributed across different physical racks or rack-equivalent fault domains. This provides higher resiliency against rack-level failures (like power loss or switch outage) in large-scale data centers.
🧱 Why Rack Fault Tolerance Matters
✅ Protection from single rack failure
✅ Improved high-availability across data center zones
✅ Essential for NIS2 compliance and modern data center design
By organizing nodes into fault domains like racks or chassis, S2D ensures data is never stranded in one failure zone.
📏 Capacity Efficiency
Rack-Level Nested Mirror (RLNM) typically uses more storage overhead compared to other configurations due to its multiple mirrored copies. For example:
A three-way mirror provides only 33% capacity efficiency, i.e., you get 1 TB of usable storage from 3 TB.
With four copies (common in RLNM), the efficiency drops to 25%.
This trade-off offers greater resiliency, especially at the rack level, making it ideal for critical workloads.
🔄 RAID Configuration in S2D
Storage Spaces Direct does not use traditional hardware RAID. Instead, it provides software-defined resiliency, which functions similarly to:
Mirror (RAID 1) — for high redundancy (used in RLNM)
Parity (RAID 5/6) — for balanced capacity and resiliency
Nested Mirror — a combination of local and cross-rack mirroring for rack fault tolerance
RLNM applies mirror-mirror configurations that can survive a rack failure and still ensure data availability.
🛡️ Resiliency Options
When creating volumes, you can choose from several resiliency settings:
Mirror — High performance, low capacity efficiency
Dual Parity — Good balance between performance and capacity
Nested Mirror (RLNM) — Highest resiliency, lowest capacity efficiency (used across racks)
You can specify resiliency during volume creation using:
New-Volume -ResiliencySettingName Mirror -PhysicalDiskRedundancy 3⚙️ Prerequisites
Windows Server 2025 Insider Build 26445 or later
Minimum 4 nodes, ideally spread across 2 racks (virtual or physical)
Domain-joined nodes
S2D-supported hardware or VMs with virtual disks
Admin access and PowerShell remoting enabled
🧪 Step 1: Install Required Features
Run this on all nodes:
Install-WindowsFeature -Name FS-FileServer, Failover-Clustering, Storage-Replica -IncludeManagementTools🌐 Step 2: Configure Network & Create Cluster
Ensure nodes are reachable and create the cluster:
New-Cluster -Name S2DCluster -Node Node1,Node2,Node3,Node4 -StaticAddress 10.0.0.100Replace Node1... with your actual server names.
🧭 Step 3: Set Fault Domains (Rack Awareness)
Define fault domains (rack1 and rack2) and map nodes:
New-ClusterFaultDomain -Name Rack1 -Type Rack
New-ClusterFaultDomain -Name Rack2 -Type Rack
Set-ClusterFaultDomain -Name Node1 -Parent Rack1
Set-ClusterFaultDomain -Name Node2 -Parent Rack1
Set-ClusterFaultDomain -Name Node3 -Parent Rack2
Set-ClusterFaultDomain -Name Node4 -Parent Rack2💾 Step 4: Enable Storage Spaces Direct
Run on the cluster node:
Enable-ClusterS2D🧱 Step 5: Create RLNM Volume
Use the following to create a 1TB resilient volume:
New-Volume -StoragePoolFriendlyName *Cluster* -FriendlyName RLNMVolume -FileSystem CSVFS_ReFS -Size 1TB -ResiliencySettingName Mirror -PhysicalDiskRedundancy 3NOTE: If your capacity drives are solid-state drives (SSD), set the -MediaType to SSD instead and change the -FriendlyName to *OnSSD. Don't modify other parameters.
Tip: Verify that Get-StorageTier created the tiers successfully.
🔎 Step 6: Validate Setup
Run the following to ensure everything is aligned:
Get-ClusterFaultDomain
Get-StoragePool
Get-VolumeStep 7: In Windows Admin Center
Volumes with nested resiliency are clearly labelled in Windows Admin Center. After creation, you can manage and monitor them like any other volume in Storage Spaces Direct.
🚫 Common Errors You Might Face
Error | Cause | Fix |
Cluster Validation Error | Misconfigured NICs or cluster network | Run Test-Cluster and fix reported issues |
S2D Not Enabling | Disk types incompatible | Use supported disk configurations |
Volume Creation Failure | Insufficient disks or wrong redundancy | Check disk count and resiliency settings |
🧯 Troubleshooting Tips
✅ Always run Test-Cluster before enabling S2D
✅ Use Get-ClusterLog -UseLocalTime for log collection
✅ Keep firmware/drivers up-to-date
✅ Monitor S2D Health via Windows Admin Center or PowerShell
🏁 Conclusion
Rack-Level Nested Mirror (RLNM) brings critical resilience to your hyper-converged clusters. By distributing mirrored data across physical racks, it eliminates a major single point of failure in enterprise environments.
Windows Server 2025 is pushing the limits of infrastructure availability — and RLNM is a key piece for future-ready, rack-aware deployments.
🧰 PowerShell Commands Summary
Install-WindowsFeature -Name FS-FileServer, Failover-Clustering, Storage-Replica -IncludeManagementTools
New-Cluster -Name S2DCluster -Node Node1,Node2 -StaticAddress 10.0.0.100
New-ClusterFaultDomain -Name Rack1 -Type Rack
Set-ClusterFaultDomain -Name Node1 -Parent Rack1
Enable-ClusterS2D
New-Volume -StoragePoolFriendlyName *Cluster* -FriendlyName RLNMVolume -FileSystem CSVFS_ReFS -Size 1TB -ResiliencySettingName Mirror -PhysicalDiskRedundancy 3🔗 Microsoft Resources
If you liked this article, do share the same. You can also Buy me a Coffee using Paypal at "paypal.me/duttaavijit", This is purely a volunteer effort. THANK YOU !!!
Comments