What Storage Spaces actually is
Storage Spaces is software-defined storage built into Windows. You group physical drives into a storage pool. From that pool you carve out virtual drives, called storage spaces. You choose a resiliency layout for each space, and Windows then shows it as an ordinary drive with a letter and a file system.
XDA notes the feature debuted in Windows 8. Microsoft's current support page says it applies to Windows 10 and Windows 11. You need at least two extra drives in addition to the one Windows is installed on. Those can be USB, SATA or SAS drives.
"RAID-like" is fair shorthand, but it is software, not a hardware RAID controller. Windows handles everything, so the "similar to RAID 1" comparison tells you about the data layout. It does not promise the same speed or behavior.
The layouts, and how many drives each needs
Microsoft's guidance maps to these options:
| Layout | Protection | Minimum drives | Microsoft's suggested use |
|---|---|---|---|
| Simple | None | 2 to be useful | Temporary data, scratch files |
| Two-way mirror | One drive failure | 2 | General-purpose storage |
| Three-way mirror | Two drive failures | 5 | General-purpose storage |
| Parity | One drive failure | 3 | Archives, streaming media |
| Dual parity | Two drive failures | 7 | Archives, streaming media |
A two-way mirror makes two copies of your files and tolerates one drive failure. A three-way mirror tolerates two failures and needs at least five drives. Microsoft also says that a mirror space formatted with ReFS gets automatic data-integrity maintenance, which adds resilience.
The USB catch
This is where the experiment gets interesting. XDA's author used an external SSD and an external HDD. Microsoft's support page warns that USB drives may not qualify. An external USB drive can work normally in File Explorer and still not appear in Storage Spaces. The feature only accepts disks that Windows recognizes as eligible physical disks.
Many USB enclosures and hubs make Windows treat drives as removable, or hide several disks behind one device identity. Storage Spaces excludes these by design, and Microsoft says this is expected behavior, not a Windows bug.
To check a drive, select the disk itself, not the volume, in Device Manager or Disk Management. Then see whether Windows reports it as Fixed or Removable. Microsoft says directly connected SATA drives are usually eligible, as are enterprise SAS drives. XDA makes a similar point: flash drives are out, and some enclosures won't present themselves correctly.
What went wrong in the reported test
The author backed up and emptied both drives first. Settings then showed neither drive as usable for Storage Spaces. Control Panel let him select them, but pool creation failed with a message that the disk's sector size was incompatible with the pool.
His fix was to check CanPool in an elevated Terminal. He ran Get-PhysicalDisk and looked for CanPool set to True. He then reset the affected disks with Reset-PhysicalDisk and rechecked. He also had to restart the PC. This is one person's result on one pair of drives. Microsoft's Storage Spaces support page does not prescribe this as a general fix for sector-size errors.
Read this before running Reset-PhysicalDisk
The command is destructive. Microsoft's documentation says that for Storage Spaces it removes the pool configuration and pool data from the specified disk. On a disk that isn't in a pool, it clears leftover Storage Spaces data and metadata. Data recovery firm Gillware goes further and tells people with a damaged pool not to run it on any remaining drive, because it can wipe the metadata needed for recovery.
Practical rules:
- Back up first, and only reset disks whose contents you can lose.
- Identify the disk by its UniqueId or FriendlyName, and confirm it is the one you mean. Use the Select FriendlyName, UniqueId output to be sure.
- Never reset a disk that belongs to a pool holding data you want.
- One troubleshooting write-up suggests reading the CannotPoolReason property first. That is a sensible way to learn why a disk is rejected before you wipe anything.
Creating the mirror
Microsoft's documented route goes through taskbar search:
- Connect the drives you want to group.
- Search for Storage Spaces on the taskbar and open it.
- Under Add a new Storage Pool, select Add.
- Name the pool, choose the drives under Add disks, and select Create.
- Name the storage space and choose a resiliency. Two-way mirror is the default.
- Set the maximum size and select Create.
- Assign a volume label and drive letter, choose a file system, and select Format.
XDA's author reached the same feature through System > Storage > Advanced storage options > Storage Spaces in Settings. Both routes lead to the same place, though menu labels can differ between Windows builds.
Mismatched drives and the capacity trap
The author used an SSD and an HDD of different sizes. He says that is not ideal for mirroring, and the arithmetic backs him up. In a two-way mirror, every file exists twice. The pool's headline size adds both disks together, but protected capacity is limited by what the smaller drive can match. Windows Central-style guides and others describe the mirror cost as roughly half of the raw capacity. XDA's screenshot shows a pool reporting 12GB in use while File Explorer shows 5.37GB of files. That gap is the duplication at work.
Performance is also an open question. XDA says mirroring may improve performance, but it concedes that software RAID may not show the clear gains of hardware RAID. Pairing a slow HDD with an SSD will not help either. Microsoft's performance claims are about workload suitability, not measured speeds on consumer hardware.
Risks beyond the setup
- A mirror is not a backup. It protects against one drive dying. It does not protect against deletion, malware, theft, fire, or anything that hits the whole PC. Keep a separate backup.
- USB mirrors can be fragile. One guide warns that a sleeping or briefly disconnected USB drive can drop out of a pool. For anything important, internal drives are the safer choice.
- Pools can be upgraded or removed. Microsoft says upgraded pools are not compatible with earlier Windows versions, which matters if you move drives between PCs. When you remove a drive, Windows copies its data to other drives in the pool. Microsoft warns this can take hours and needs enough free space in the pool.
Verdict
Storage Spaces is a legitimate, low-friction way to get drive redundancy on Windows 10 and 11 without touching BIOS RAID. For a test with spare drives, XDA's walkthrough shows it works. For real data, use matched internal drives where you can. Check that Windows sees your disks as eligible before you plan around them. Treat Reset-PhysicalDisk as a last resort, because it is the one step in this story that can destroy data.