Connecting multiple backup drives together lets you create a single, larger backup volume instead of juggling separate drive letters and manual file splitting. When done correctly, Windows treats two or more physical USB or SATA drives as one logical pool, so your backup software sees one destination, redundancy can be configured, and you avoid running out of space on a single drive mid-backup. This guide shows you how to do it with Windows Storage Spaces, the built-in tool for drive pooling, without third-party RAID hardware.
Prerequisites: You should be running Windows 10 or Windows 11 on an administrator account, have your backup drives empty or have already copied any data you want to keep elsewhere, and have all drives connected directly to the PC rather than through an unpowered hub. As of 2026, the classic Control Panel Storage Spaces workflow remains the most stable way to build a pool for backup use.
Before You Start
| What you need | Why | Optional? |
|---|---|---|
| 2 to 4 external drives of similar size (USB 3.0 or faster, NTFS or unformatted) | The pool stripes or mirrors data across them so matched capacities prevent wasted space | No |
| Powered USB hub or direct motherboard USB ports | Prevents disconnects during pool creation which can corrupt the virtual disk | Yes if you have enough native ports, No if using more than two bus-powered drives |
| Administrator account | Required to create pools and format virtual disks in Storage Spaces | No |
| Backup software paused or closed (Windows Backup, File History, Macrium, Veeam Agent) | Prevents file locks that block formatting | No |
| SATA or NVMe drive dock for internal drives | Lets you pool bare 3.5-inch drives without an enclosure | Yes |
| Label maker or masking tape and marker | To physically label which drive corresponds to which pool member | Yes |
Back up any existing data on the drives you plan to pool. Creating a pool removes all partitions and formats the drives. If a drive shows as RAW, exFAT, or has existing backups, copy its contents to a separate location like C:\Backup_Temp\ before you begin. Confirm all drives appear in Disk Management at Computer Management > Storage > Disk Management or by pressing Win + X > Disk Management. Each should show as Online and either Unallocated or with a healthy partition you are willing to erase.
Step-by-Step
Step 1: Prepare and clean the drives – Time: 5 to 10 minutes
Press Win + R, type diskmgmt.msc, and press Enter. Right-click each backup drive and select Properties > Volumes tab to confirm capacity and connection type. If any drive contains partitions you no longer need, right-click the partition > Delete Volume. Do this for every volume on the drives you will pool until each shows as Unallocated. Do not initialize to MBR or GPT yet if prompted; Storage Spaces will handle it. Leave the drives connected and close Disk Management.
Step 2: Open Storage Spaces – Time: 1 minute
Press Win + S, type Control Panel, and open it. Navigate to Control Panel > System and Security > Storage Spaces. If you are on Windows 11, you can also go to Settings > System > Storage > Advanced storage settings > Storage Spaces, then click the link to open the classic Control Panel view for full pool creation options. Click Create a new pool and storage space and approve the User Account Control prompt.
Step 3: Create the storage pool – Time: 2 minutes
In the Storage Spaces window you will see a checkbox next to each eligible drive. Check the boxes for the 2 to 4 drives you prepared. The capacity summary at the bottom shows total pool capacity. Click Create pool. Windows will create a pool named Storage pool by default, visible at C:\Windows\System32\StorageSpaces\ as pool metadata. This step is instant and does not format yet, so you can still cancel without data loss until the next step.
Step 4: Create the virtual drive for backups – Time: 3 to 5 minutes
After pool creation you are taken to the Create a storage space dialog. Set the following: Name: BackupPool, Drive letter: choose E: or the next available, File system: NTFS, Resiliency type: choose Simple (no redundancy, maximum space) if you want capacity, or Two-way mirror if you want protection against one drive failure and have at least two drives. Storage type for NTFS on a simple pool defaults to thin provisioning. For Size (maximum): enter the full pool capacity shown, for example 3725 GB for two 2 TB drives, or set a smaller value like 2000 GB if you want to leave space for another virtual disk later. The Size can be larger than physically available when using Thin provisioning, but keep it at or below physical total for backup stability. Click Create storage space.
Step 5: Format and assign settings – Time: 1 to 2 minutes
Windows automatically formats the new virtual disk. When finished, open File Explorer with Win + E and confirm the new drive appears under This PC. Right-click the new drive > Properties > General tab to verify File system: NTFS and capacity. Go to Properties > Hardware tab to confirm the device name shows Microsoft Storage Space Device. If the drive does not appear, press Win + X > Disk Management and ensure the virtual disk shows as Online and Healthy. Assign a volume label like BackupPool so backup software can find it consistently.
Step 6: Configure backup software to use the pooled drive – Time: 5 minutes
Open Windows Backup via Settings > System > Storage > Advanced storage settings > Backup options or open File History at Control Panel > System and Security > File History. Click Select drive or Add a drive and choose the new pooled drive letter (E:). For File History, click Turn on, then Advanced settings > set Save copies of files to Every hour and Keep saved versions to Until space is needed. For third-party tools like Macrium Reflect, go to Create a backup > Destination > Browse > select E:\ and set the file location to E:\Backups\. Run a manual backup of a small folder such as C:\Users\YourName\Documents\Test\ to confirm write access.
Step 7: Set power and sleep exclusions – Time: 2 minutes
Go to Settings > System > Power > Screen and sleep and set When plugged in, put my device to sleep after to Never during initial backup. Then go to Control Panel > Hardware and Sound > Power Options > Edit Plan Settings > Change advanced power settings > expand USB settings > USB selective suspend setting > set to Disabled. Expand Hard disk > Turn off hard disk after > set to 0 or Never for the backup window. This prevents drives from spinning down mid-pool write. Restore your preferred sleep settings after the first full backup completes.
Verify It Worked
Open Control Panel > System and Security > Storage Spaces. You should see the pool with all drives listed as OK and the storage space listed with its resiliency type, capacity, and usage percentage. Copy a test folder of at least 5 GB to the pooled drive and check that free space decreases on the pool summary, not on an individual physical drive.
Press Win + R, type powershell, and press Enter. Run Get-StoragePool and Get-VirtualDisk. Get-StoragePool should return FriendlyName: Storage pool, OperationalStatus: OK, HealthStatus: Healthy. Get-VirtualDisk should return FriendlyName: BackupPool, ResiliencySettingName: Simple or Mirror, OperationalStatus: OK. In Event Viewer, navigate to Applications and Services Logs > Microsoft > Windows > StorageSpaces-Driver > Operational and confirm no Error events in the last hour. Finally, disconnect and reconnect the USB cable for the pooled drive enclosure with the PC powered on and confirm the pooled volume remounts automatically within 10 to 20 seconds in File Explorer.
Mistakes to Avoid
Mixing drive sizes without understanding thin provisioning. What causes it: Adding a 1 TB drive to a pool with a 4 TB drive creates uneven utilization and the pool warns about reduced efficiency. How to check: In Control Panel > System and Security > Storage Spaces, look at pool capacity versus physical drives listed. If capacities vary by more than 25 percent, you will see wasted space. What to do: Use drives within 10 to 20 percent of the same capacity, or create a separate pool for mismatched sizes. How to undo: Go to Storage Spaces > Change settings > Physical drives > Prepare for removal > Remove for the mismatched drive, then delete the virtual disk and recreate the pool.
Creating the pool while File History is still writing. What causes it: File History locks E:\FileHistory\ and prevents formatting, causing the error Cannot create storage space. How to check: Open Task Manager with Ctrl + Shift + Esc > Processes tab and see if FileHistory.exe or backup service is active, or check C:\Users\YourName\AppData\Local\Microsoft\Windows\FileHistory\ for recent writes. What to do: Turn off File History via Control Panel > System and Security > File History > Turn off before creating the pool, then re-enable after. How to undo: If creation failed, delete the incomplete storage space in Storage Spaces, restart the PC, and recreate after disabling the backup service.
Using an unpowered USB hub for multiple drives. What causes it: Bus-powered hubs cannot supply stable 900 mA per port, leading to intermittent drive disconnects that mark the pool as Degraded. How to check: In Storage Spaces the physical drive status changes to Warning or Lost Communication, and Event Viewer > System shows disk errors with source Disk. What to do: Move drives to motherboard USB ports or a powered hub rated at 12V 3A or higher, and set USB selective suspend to Disabled as in Step 7. How to undo: Reconnect the drive, go to Storage Spaces > Physical drives > select the affected drive > mark as OK if available, or remove and re-add the drive to rebuild the pool.
Choosing Two-way mirror with only two drives and then expecting to expand later. What causes it: Two-way mirror requires at least two drives and reserves half the capacity for duplication, so adding a third drive later does not automatically expand usable space without recreation. How to check: In Storage Spaces, the storage space shows Resiliency: Two-way mirror and Size close to 50 percent of pool capacity. What to do: If you plan to add drives later for capacity, use Simple with an external second copy for redundancy, or plan to create a new mirror only when you have three matched drives. How to undo: Back up data from E:\ to another location, go to Storage Spaces > Delete the storage space > recreate with the desired resiliency type and restore data.
FAQ
Can I add another drive to the pool after it is created?
Yes. Go to Control Panel > System and Security > Storage Spaces > Add drives. Check the box for the new unformatted drive and click Add drive. The pool capacity increases immediately. To extend the virtual disk, select the storage space > Change > extend Size up to the new pool capacity. If you use Simple resiliency, no rebuild is needed. If you use Two-way mirror, the system automatically begins an optimization pass visible as OperationalStatus: Rebalancing when you run Get-StorageJob in PowerShell.
Do the drives need to be the same brand or model?
No, but they should have similar interface speed and sector size. Mixing 512e and 4Kn sector drives can prevent pool creation. Check sector size by opening Command Prompt as administrator and running fsutil fsinfo sectorInfo E:. Compare BytesPerPhysicalSector values. If they differ, replace the outlier drive with a matching sector format. Brand and RPM do not matter for USB pooling, though mixing a slow USB 2.0 drive with USB 3.0 drives will limit overall pool throughput to the slowest member during writes.
Will connecting drives together erase them?
Yes, for the initial pool creation. The step Create pool deletes partitions on all selected drives. Storage Spaces warns you with the message Selecting these drives will erase all data. After the pool exists, adding a new drive also erases that new drive only, not the data already on the pooled volume. Always copy data from the drives to C:\Backup_Temp\ or another safe disk before you begin, and verify the copy by checking Properties > size and file count.
What happens if one drive fails in a pooled backup?
It depends on resiliency. With Simple, the entire pooled volume becomes inaccessible and shows OperationalStatus: Detached in PowerShell, and you must restore from a separate backup. With Two-way mirror, the pool shows HealthStatus: Warning and the virtual disk remains accessible on the remaining drive. Replace the failed drive, go to Control Panel > System and Security > Storage Spaces > Physical drives > mark the failed drive as retired, add the new drive via Add drives, and the system rebuilds the mirror automatically. Check rebuild progress with Get-StorageJob in PowerShell until PercentComplete reaches 100.
