Introduction

RAID (Redundant Array of Independent Disks) is designed to improve storage reliability, performance, and redundancy. However, disk failures, data corruption, and array degradation can still occur. This guide provides an introductory approach to diagnosing and resolving RAID disk issues effectively.

Common RAID Issues and Symptoms

1. Degraded RAID Array

If your RAID is operational but running in degraded mode due to a failed disk, then you can check the following

cat /proc/mdstat
sudo mdadm --detail /dev/md0

Here you can identify the failed disk and replace it with a new one.

2. Failed RAID Rebuild

If the RAID rebuild fails to complete, or the array remains degraded, then you can check the mdraid details

sudo mdadm --detail /dev/md0

Go for the logs to check something is logged related to mdraid or disk failure. You can also consult to dmesg command.

sudo dmesg | grep md

Verify disk health using SMART diagnostics and retry the rebuild.

3. RAID Not Detecting a New Disk

If a replacement disk is not recognized by RAID then you can go through the following

1. Check if the system detects the disk

   lsblk
   fdisk -l
   

2. If not, check physical connections and power cycle the system, or better to shutdown, wait for a minute and power-on your system. PS: If your system has configuration console like iDRAC, iLO etc. it is also adviced to check the physical state of the disks. For example, a reseat might be needed accordingly.
3. Add the disk manually

   sudo mdadm --add /dev/md0 /dev/sdb
   

4. Disk Errors and Bad Sectors

If your RAID rebuilds slowly, and logs show read/write errors, then checking the smart values would be a nice start for the troubleshooting.

sudo smartctl -a /dev/sdb

Look for attributes like Reallocated Sectors Count and Pending Sectors as well as check if any Correctable/Uncorrectable Errors counters are increasing. Such problems are usual suspects of performance related recovery issues. If bad sectors increase, go ahead and replace the disk.

5. RAID Array Not Assembling on Boot

An annoying problem which hits during the boot like your RAID fails to mount or appears inactive after reboot. What you can do here can be ordered as follows

1. Check RAID status and scan the raid

   sudo mdadm --detail /dev/md0
   sudo mdadm --assemble --scan
   

2. Ensure mdadm.conf is correctly configured, any misconfiguration can cause mdraid not working properly.

   sudo mdadm --detail --scan >> /etc/mdadm/mdadm.conf
   

3. Rebuild the initramfs and update the boot configuration:

   sudo update-initramfs -u
   sudo update-grub
   

6. Data Corruption in RAID

Wishing that nobody has a Data Corruption never ever, but it happens unfortunately and lets assume files are unreadable or produce errors. You can initially check filesystem errors

dmesg | grep EXT4-fs

and if there is any you can proceed with a filesystem check

1. Run a filesystem check

   sudo fsck -y /dev/md0
   

2. Scrub RAID for silent corruption

   echo check > /sys/block/md0/md/sync_action
   

Monitoring RAID Health

Monitoring RAID health is crucial to ensuring data integrity, system reliability, and early detection of potential disk failures. Regular monitoring helps identify degraded arrays, failing disks, and performance bottlenecks before they lead to catastrophic data loss or downtime. By keeping track of RAID status, disk health, and system logs, administrators can proactively replace failing drives, prevent data corruption, and optimize rebuild times, ultimately maintaining system stability and reducing the risk of unexpected failures.

Using mdadm

to check real-time RAID status you can simply use watch command to see the progress.

watch cat /proc/mdstat

Monitor detailed array information

sudo mdadm --detail /dev/md0

SMART Disk Monitoring

It is important to run periodic health checks

sudo smartctl -t long /dev/sdb

Log File Analysis

Always check the system logs for RAID errors

sudo journalctl -u mdadm
sudo dmesg | grep md

Preventive Measures

• Regular Backups: RAID is not a substitute for backups.
• Automated RAID Health Monitoring:

sudo mdadm --monitor --scan --daemonize --syslog

• Scheduled Scrubbing:

echo check > /sys/block/md0/md/sync_action

• Use Enterprise-Grade Disks: Consumer-grade drives can fail under RAID workloads.

Conclusion

Troubleshooting RAID issues requires proactive monitoring, timely disk replacements, and understanding system logs. By following this guide, administrators can ensure RAID arrays remain operational and recover effectively from failures.

Would you like a script for automated RAID health checks? Let us know!