Detecting Bad Blocks on Storage Devices

If you suspect a disk has bad blocks, use the badblocks utility to scan for them. This tool probes a device (usually a disk partition) and reports which blocks are unreliable or unreadable.

Basic Usage

badblocks /dev/sda1

This scans /dev/sda1 from the first block to the last block on the device.

Common Options

• -s: Show progress (recommended for large disks)
• -v: Verbose output
• -w: Perform a destructive write test (overwrites data — use only on blank/backup disks)
• -n: Non-destructive read-write test (safer, but slower)
• -f: Force the test even if the device appears mounted
• -b block_size: Specify block size in bytes (default: 4096)
• -c blocks_at_once: Number of blocks to test at once (default: 16)
• -p num_passes: Number of test passes (default: 0, runs until interrupted)
• -t test_pattern: Use a specific test pattern (0, 1, 2, 3, or random)
• -e max_bad_blocks: Stop after finding this many bad blocks
• -o output_file: Write bad block numbers to a file
• -i input_file: Read bad block list from a file

Examples

Non-destructive read test on a mounted partition:

sudo badblocks -s -n /dev/sda1

Write-destructive test (warns: data will be overwritten):

sudo badblocks -s -w /dev/sda1

Test a specific range (blocks 1000 to 5000):

sudo badblocks -s /dev/sda1 5000 1000

Save results to a file:

sudo badblocks -s -o bad_blocks.txt /dev/sda1

Important Considerations

• Root access required: badblocks needs root privileges to access raw device blocks.
• Don’t run on mounted filesystems with -w flag; you’ll corrupt data. Use -n instead for non-destructive testing on live systems.
• Slow on large disks: Full scans of multi-terabyte drives take hours. Consider testing specific ranges or increasing -c for speed.
• Modern SSDs: badblocks is primarily designed for HDD testing. Modern SSDs have built-in SMART monitoring and wear-leveling that makes traditional bad block testing less relevant.

Integration with Filesystem Tools

After identifying bad blocks, use fsck with the bad block list to mark them as unusable:

sudo fsck -l bad_blocks.txt /dev/sda1

Alternatively, e2fsck for ext2/3/4 filesystems:

sudo e2fsck -l bad_blocks.txt /dev/sda1

Checking SMART Data First

Before running badblocks, check your drive’s SMART status to see if the manufacturer already detected issues:

sudo smartctl -a /dev/sda

This is faster and won’t risk further disk stress if the drive is already failing.

Additional Tips and Best Practices

When implementing the techniques described in this article, consider these best practices for production environments. Always test changes in a non-production environment first. Document your configuration changes so team members can understand what was modified and why.

Keep your system updated regularly to benefit from security patches and bug fixes. Use package managers rather than manual installations when possible, as they handle dependencies and updates automatically. For critical systems, maintain backups before making any significant changes.

Quick Verification

After applying the changes described above, verify that everything works as expected. Run the relevant commands to confirm the new configuration is active. Check system logs for any errors or warnings that might indicate problems. If something does not work as expected, review the steps carefully and consult the official documentation for your specific version.