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Storage Spaces on Windows: software RAID without the marketing

Verified 2 min read

Build a pool, choose mirror or parity, understand why parity writes are slow, and know the cases where Storage Spaces is the wrong tool.

Tested onPro (26H2) / Server · Build 26300.9457 / 26100.33650 · x64
E1
Build
26300.9457 / 26100.33650
Edition
Pro (26H2) / Server
Architecture
x64
Support
Documentation (E1)
Evidence
E1Official documentation
Verified
2026-10-29
Page type
Task

The short answer

Section titled “The short answer”

Storage Spaces pools physical disks and presents one or more virtual disks with simple, mirror or parity resiliency.

  • Mirror is fast and survives a disk failure at 50% usable capacity.
  • Parity uses capacity efficiently and is slow for writes — it computes parity on every write.
  • Simple has no redundancy; it is a volume manager, not a RAID.

It is the right tool for bulk data on Windows. It is not a replacement for a hardware RAID controller in a database server, and it is not Storage Spaces Direct (which is a clustered, server-grade feature).

Before you start

Section titled “Before you start”
  • Use dedicated disks. Adding a disk with data destroys it.
  • Prefer identical disks per pool; mixed sizes waste capacity or reduce resiliency.
  • Do not pool the boot disk.
  • Have a backup. Resiliency protects against a dead disk, not against deletion or ransomware.
Terminal window
Get-PhysicalDisk | Select-Object FriendlyName,MediaType,BusType,Size,CanPool,HealthStatus

CanPool : False usually means the disk holds a partition (including a stray recovery partition). Clear it deliberately, or use a different disk.

Build a mirrored pool

Section titled “Build a mirrored pool”
Terminal window
# 1. pool
$disks = Get-PhysicalDisk -CanPool $true
New-StoragePool -FriendlyName DataPool -StorageSubSystemFriendlyName 'Windows Storage*' -PhysicalDisks $disks


# 2. virtual disk (mirror, fixed provisioning is predictable)
New-VirtualDisk -StoragePoolFriendlyName DataPool -FriendlyName DataMirror `
  -ResiliencySettingName Mirror -Size 2TB -ProvisioningType Fixed


# 3. volume + filesystem
Get-VirtualDisk DataMirror | Get-Disk | Initialize-Disk -PartitionStyle GPT
New-Partition -DiskNumber (Get-VirtualDisk DataMirror | Get-Disk).Number -UseMaximumSize -DriveLetter D
Format-Volume -DriveLetter D -FileSystem NTFS -NewFileSystemLabel Data -Confirm:$false

For parity, change -ResiliencySettingName to Parity. Expect much lower write throughput and plan the workload accordingly.

Resiliency settings that matter

Section titled “Resiliency settings that matter”
Setting Effect
PhysicalDiskRedundancy How many disks may fail (1 or 2)
NumberOfColumns Stripes across disks; more columns = more throughput, fewer disks can fail
Interleave Stripe unit size; defaults are usually fine
ProvisioningType Fixed predictable, Thin over-commits

Two-way mirror on two disks gives you one disk of usable capacity and survives one failure. Three-way mirror needs five disks for the same usable capacity. Do the arithmetic before buying disks.

Check health and rebuilds

Section titled “Check health and rebuilds”
Terminal window
Get-StoragePool | Select-Object FriendlyName,HealthStatus,OperationalStatus,Size,AllocatedSize
Get-VirtualDisk | Select-Object FriendlyName,ResiliencySettingName,HealthStatus,OperationalStatus
Get-PhysicalDisk | Select-Object FriendlyName,HealthStatus,OperationalStatus,Usage

A degraded virtual disk still serves data but has no redundancy left. Replace the failed disk and let the pool repair; do not remove a second disk “to see what happens”.

Where Storage Spaces is wrong

Section titled “Where Storage Spaces is wrong”
  • Boot volume — not supported on client Windows.
  • Database with random writes — parity is unsuitable; mirror or hardware RAID.
  • Mixed USB drives — removable and unreliable; a single glitch can drop the pool.
  • Storage Spaces Direct — that is a different feature requiring a cluster and certified hardware; do not follow S2D guides for a desktop pool.

ReFS on a pool

Section titled “ReFS on a pool”

ReFS on a Storage Spaces volume gives you integrity streams and faster repair in some scenarios, but:

  • it is not bootable on client Windows;
  • some applications (and some backup tools) behave differently;
  • it is not a substitute for backups.

Use NTFS unless you specifically need ReFS features.

Section titled “Related”

Lab boundary

Section titled “Lab boundary”

E1. The cmdlets are Microsoft-documented; the lab’s virtual machines have not had a Storage Spaces pool created for this page, so no pool performance is claimed.

Sources