{"id":17380,"date":"2026-02-20T11:19:35","date_gmt":"2026-02-20T05:49:35","guid":{"rendered":"https:\/\/www.skynats.com\/blog\/?p=17380"},"modified":"2026-02-20T11:19:38","modified_gmt":"2026-02-20T05:49:38","slug":"how-to-restore-a-failed-disk-in-a-linux-mdadm-raid1-array","status":"publish","type":"post","link":"https:\/\/www.skynats.com\/blog\/how-to-restore-a-failed-disk-in-a-linux-mdadm-raid1-array\/","title":{"rendered":"How to Restore a Failed Disk in a Linux mdadm RAID1 Array"},"content":{"rendered":"\n

Software RAID (mdadm) on Linux<\/mark><\/a> protects your data by keeping identical copies of partitions across multiple disks in a RAID1 setup. When one of these disks fails, the array becomes degraded, meaning it still works but no longer has redundancy. It\u2019s important to fix such failures quickly to avoid data loss and Restore Failed Disk in Linux mdadm RAID1 promptly to maintain full redundancy and data protection.<\/p>\n\n\n\n

Introduction<\/strong><\/h2>\n\n\n\n

Linux software RAID provides mirrored storage using tools like mdadm, which assembles and manages RAID arrays. A RAID1 array mirrors data across two or more disks so that if one disk fails, the system continues to operate from the remaining disk without data loss. Monitoring tools report RAID health, and in degraded conditions, administrators must take action to restore redundancy.<\/p>\n\n\n\n

Step-by-Step: Repairing a Degraded RAID<\/h2>\n\n\n\n

1. Check RAID Status<\/strong><\/h2>\n\n\n\n

To begin, inspect the current RAID health:<\/p>\n\n\n\n

# cat \/proc\/mdstat<\/code><\/pre>\n\n\n\n
This will show arrays and whether a member is missing (e.g., showing [2\/1] [_U]), meaning one of two disks is not active.<\/p>\n\n\n\n
2. Identify the Failed Drive<\/strong><\/h3>\n\n\n\n
Use mdadm –detail to find which device is marked as failed:<\/p>\n\n\n\n
#mdadm --detail \/dev\/md0<\/code><\/pre>\n\n\n\n
Look for devices with (F) or removed status. These are candidates for rebuild or replacement.<\/p>\n\n\n\n
3. Remove Failed Drives<\/strong><\/h3>\n\n\n\n
If a disk has actually failed and is still in the RAID metadata, mark it as failed and remove it:<\/p>\n\n\n\n
#mdadm --manage \/dev\/md0 --fail \/dev\/nvme0n1p3<\/code><\/pre>\n\n\n\n
#mdadm --manage \/dev\/md0 --remove \/dev\/nvme0n1p3<\/code><\/pre>\n\n\n\n
This cleans up the array and prepares it for the replacement device.<\/p>\n\n\n\n
4. Re-Add a Disk to the Array<\/strong><\/h3>\n\n\n\n
If a disk was removed but is actually intact and was part of the array recently, you can use mdadm –re-add. This tells mdadm to add back a device that was previously part of the RAID, using its existing metadata and event count to re-synchronize.<\/p>\n\n\n\n
Example:<\/p>\n\n\n\n
#mdadm --manage \/dev\/md0 \/dev\/nvme1n1p1 --re-add<\/code><\/pre>\n\n\n\n
This instructs the driver to reinsert the disk into the same RAID slot it previously occupied, triggering recovery if needed.<\/p>\n\n\n\n
Use cases for –re-add:<\/p>\n\n\n\n