How to set up RAID 1

RAID 1 mirrors data across two or more disks, allowing the array to remain available if one member fails, as long as another copy is healthy. This guide covers setting up RAID 1 on Windows 10 and Linux, verifying the mirror, and removing it when necessary. Back up your data before changing the disk layout: a mirror also copies deletions and corruption, and a disk failure can still disrupt work during recovery.

What RAID 1 protects

RAID 1, or disk mirroring, stores copies of data on multiple members. It can suit workloads where availability after a drive failure matters and the capacity cost is acceptable. Choose the layout based on the workload and recovery requirements.

With RAID 1, the array can continue serving data after a drive fails as long as another member remains healthy. Check the surviving copy and your backup before attempting to recover data from a RAID drive, replace the failed disk, and rebuild the array. A rebuild does not guarantee protection from further errors or data loss. A mirror is not a backup: it also copies deletions and corruption. Keep separate backups alongside it.

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Linux (Ubuntu Example)

1. 1. Prepare Your Drives: As on Windows 10, use two drives of the same size and back up any existing data. Identify the exact device names with

   lsblk -o NAME,SIZE,MODEL,SERIAL

   and record them. Creating the array overwrites the disks you specify.
2. 2. Install mdadm: Open Terminal and install mdadm with:

sudo apt update

sudo apt install mdadm

1. 3. Partition Your Drives (Optional): Use fdisk or gdisk to create partitions if needed. Make sure both partitions are the same size and set their type to "Linux RAID" (fd in fdisk, fd00 in gdisk).
2. 4. Create a RAID 1 Array:

• After verifying both member devices, run the following command on one line:

sudo mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdX1 /dev/sdY1

• Replace /dev/sdX1 and /dev/sdY1 with the actual drive or partition identifiers, and check them again before pressing Enter. Pointing the command at the wrong device overwrites it.

1. 5. Verify the Array Creation:

• Check the status with:

cat /proc/mdstat

• This shows active RAID devices, their members, and synchronization progress. The [UU] state means both members are healthy. You can also run

  sudo mdadm --detail /dev/md0

  for a detailed report. Let the initial resync complete before storing important data on the mirror.

1. 6. Create a Filesystem:

• Format the array with a filesystem, e.g., ext4:

sudo mkfs.ext4 /dev/md0

1. 7. Mount the RAID Array:

• Create a mount point and mount the array:

sudo mkdir -p /mnt/raid1

sudo mount /dev/md0 /mnt/raid1

• To mount the array automatically at boot, add it to /etc/fstab using the UUID reported by

  sudo blkid /dev/md0

  , for example: UUID=your-uuid /mnt/raid1 ext4 defaults 0 0.

1. 8. Configure mdadm for Boot:

• Save the array definition so mdadm can identify and assemble it at startup. Check the existing file before appending another ARRAY entry:

sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf

sudo update-initramfs -u

How to Remove the RAID

If you want to stop using RAID storage and return to conventional single-drive setups, you can do so whether you set up RAID 1 on Windows 10 or Linux. Copy your files off the array first, because clearing RAID metadata or deleting volumes can make data inaccessible. Whether repartitioning and formatting are necessary depends on the implementation and intended reuse.

On Linux

Run these commands to unmount the array, stop it, and clear RAID metadata from each member:

• sudo umount /dev/md0

  
  

  sudo mdadm --stop /dev/md0

  
  

  sudo mdadm --zero-superblock /dev/sdX1 /dev/sdY1

  (replace /dev/sdX1 and /dev/sdY1 with your actual members)

Edit the mdadm.conf file to remove the ARRAY definition saved earlier, then run

sudo update-initramfs -u

so the next boot does not try to assemble the old array.

Also edit /etc/fstab to disable the auto-mount entry you activated. Otherwise, boot may stall while the system waits for a device that no longer exists.

On Windows 10:

If your RAID 1 is a Disk Management mirrored volume, right-click one half of the mirror and select "Remove Mirror". Select "Break Mirror" instead if you want to retain both copies, then delete the remaining volumes. If you created RAID 1 with Windows Storage Spaces, delete the “Pool” to remove the RAID:

• Open Windows Storage Spaces through Settings → System → Storage → Manage Storage Spaces, or search the Start menu for "Storage Spaces".
• After verifying the backup, delete the storage space or spaces in the pool, then delete the empty pool using the options available in that Windows version.
• Confirm the action. The drives then return to unallocated space that you can format for single-drive use.

Before removing RAID 1, make sure you have backed up all files and data stored on the RAID. You can use professional data backup software compatible with the Windows 10 OS version on your PC.

If you find missing files or data after dismantling your RAID 1 array, recover them from your backup or use DiskInternals RAID Recovery software. DiskInternals RAID Recovery supports a range of RAID layouts and filesystems. Recovery depends on readable source data and whether deleted blocks have been overwritten. Verify support for the actual layout before scanning.

Can I Create a RAID 1 Array With a Drive that Already has Data?

Use an implementation-specific migration procedure and a verified backup, rather than a generic new-array command. Creating a new mdadm RAID 1 array writes RAID metadata and starts synchronization; creating a filesystem is a separate step. These operations can overwrite existing data, so do not run them on the only copy of your files. If you add a drive that still contains files to a new RAID 1 setup, you may lose all data on that drive. The same applies when you install a replacement for a failed member, because the rebuild overwrites the incoming disk. Windows' "Add Mirror" can preserve an eligible existing volume while synchronizing it to a second disk. An mdadm migration can instead start with a degraded array on an empty disk, copy the data, and add the former source disk afterward. Both workflows require a verified backup and careful device selection. A new mdadm array does not preserve existing data simply because "missing" is specified.

To be safe, make a full backup that copies all files and data from the drive in question, let the RAID 1 setup erase and initialize it, and then restore your files to the completed mirror. Keep the backup until the array reports healthy and you have spot-checked the data. When removing the mirror, follow the documented procedure for that implementation and retain the independent backup until the files are verified.

FAQ

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