Software⏱️ 3 min read📅 2026-06-15

How to Fix: RAID5 mdadm faulty / blk_update_request: I/O error

mdadm RAID5 issue with I/O errors and write permission denied.

Quick Answer: Run `sudo mdadm --zero-superblock --force` on each device, then assemble the RAID array again.

📋 Table of Contents

  1. ⚠️ Common Causes
  2. 🚀 How to Resolve This Issue
  3. ✨ Wrapping Up

The RAID5 array is faulty, causing an I/O error on sector 16 and preventing write operations to mapped devices. This issue affects users who rely on the RAID5 array for data storage.

This problem can be frustrating as it prevents the user from accessing their data stored in the RAID5 array. However, by following the steps outlined below, you should be able to resolve the issue and regain access to your data.

⚠️ Common Causes

  • The primary reason for this error is that the RAID5 array is faulty due to a hardware failure or corruption of the metadata. The `mdadm` command is unable to write to the array because it detects an I/O error on sector 16, which indicates a problem with one or more of the disks in the array.
  • Another possible cause is that the `--zero-superblock` option is not suitable for this situation. When used with `mdadm`, this option can overwrite the superblock of a RAID5 array without checking its integrity, potentially causing further damage.

🚀 How to Resolve This Issue

Reassemble and correct the metadata

  1. Step 1: Stop any ongoing data writes to the disks using `sync` or `dd if=/dev/zero of= bs=4096`. This will ensure that no further corruption occurs.
  2. Step 2: Use `mdadm --examine -a /dev/md0` to check the integrity of the metadata. If all member devices are in a clean state, checksum is correct, and event numbers are equal, then proceed with reassembly.
  3. Step 3: Run `mdadm --rebuild --force /dev/md0` to rebuild the RAID5 array from scratch. Be aware that this may overwrite existing data on the disks.

Use a different method to assemble the RAID5 array

  1. Step 1: Try using `mdadm --create --verbose /dev/md0 --level=5 --raid-type=5 /dev/sdX1 /dev/sdY1` with the `--force` option. This may overwrite existing metadata and rebuild the array from scratch.
  2. Step 2: Alternatively, use `mdadm --create --verbose /dev/md0 --level=5 --raid-type=5 --assume-clean /dev/sdX1 /dev/sdY1`. However, this method assumes that the disks are clean and free of corruption, which may not be the case in your situation.

✨ Wrapping Up

Once you have reassembled or rebuilt the RAID5 array, verify its integrity using `mdadm --examine -a /dev/md0` and check for any remaining errors. If the issue persists, consider seeking further assistance from a data recovery expert.

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