Recover Data from Crashed Disks with ddrescue command: A Comprehensive Guide

Introduction

Learn how to recover data from crashed disks using the ddrescue command in Linux. This step-by-step guide will help you rescue valuable data, solve mounting errors, and ensure your filesystem's integrity on CentOS 7.

Data loss can be a nightmare, especially when it involves critical files and documents. In the world of Linux, there are powerful tools designed to mitigate such risks. One such tool is `ddrescue`, a command-line utility that specializes in rescuing data from damaged disks. Whether you're dealing with I/O errors or corrupted filesystems, `ddrescue` offers a reliable solution to recover data from crashed disks.

In this guide, we will explore how to use the `ddrescue` command to recover data from a failed disk on a CentOS 7 server. We will also address common mounting errors, such as the "wrong fs type, bad option, bad superblock" error, and provide solutions to resolve these issues.

What is ddrescue and Why Use It?

`ddrescue` is a GNU utility that copies data from one file or block device (like a hard drive) to another. It is designed to recover data from disks that have bad sectors or other forms of damage. Unlike other data recovery tools, `ddrescue` prioritizes good sectors first and skips over the bad ones, ensuring that as much data as possible is salvaged.

Key Features of ddrescue:

- Efficient Data Recovery: Attempts to recover good data first before focusing on bad sectors.

- Flexible Options: Allows for multiple retries and direct disk-to-disk copying.

- Error Logging: Keeps a log of bad sectors and errors, allowing for easy tracking and retries.

Problem: "wrong fs type, bad option, bad superblock" Error

Understanding the Error

When trying to mount a filesystem, you might encounter the following error message:

mount: wrong fs type, bad option, bad superblock on 192.168.1.155:/home/shared, missing codepage or helper program, or other error (for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount.<type> helper program)

This error suggests that the filesystem on the disk may be corrupted or incompatible with the current mount options. It can also indicate that the system is missing necessary helper programs to mount certain types of filesystems.

Diagnosing the Issue

To diagnose the problem, start by checking the system logs for more detailed information:

dmesg | tail

This command will display the latest system messages, which can provide insights into why the mount operation failed.

Common Causes and Solutions

1. Corrupted Filesystem: If the filesystem is damaged, you may need to run fsck (File System Consistency Check) to repair it.
2. Missing Helper Programs: For certain filesystems like NFS or CIFS, you might need to install additional packages or helpers.
3. Incorrect Mount Options: Ensure that the mount options you're using are appropriate for the filesystem type.

Example Scenario: Recovering Data from a Crashed Disk

Server Configuration

Let's assume you have a CentOS 7 server with the following configuration:

• OS: CentOS 7
• HDD1: /dev/sda1
• HDD2: /dev/sdb1 (Mount point /mnt)
• HDD3: /dev/sdc1 (Newly attached disk for recovery)

In this scenario, HDD2 (/dev/sdb1) has crashed and is no longer mountable at /mnt. We'll use ddrescue to recover the data from /dev/sdb1 and copy it to a new disk, /dev/sdc1.

Step 1: Install ddrescue on CentOS

Before you can use ddrescue, it needs to be installed on your system. Run the following command to install ddrescue:

sudo yum install ddrescue -y

Step 2: Using ddrescue to Recover Data

Once ddrescue is installed, you can proceed with the data recovery process.

Command to Rescue Data

Use the following command to start the data recovery process:

sudo ddrescue -f -n /dev/sdb /dev/sdc logfile

Here’s what the command does:

• -f: Forces ddrescue to overwrite the output file if it exists.
• -n: Skips over bad sectors initially and tries to copy the good sectors first.
• /dev/sdb: The source disk (the crashed disk).
• /dev/sdc: The destination disk (the new disk).
• logfile: A file that logs the progress and errors during the recovery process.

Retry Bad Sectors

If there are additional read errors, you can retry the bad sectors with the following command:

sudo ddrescue -d -f -r3 /dev/sdb /dev/sdc logfile

• -r3: Retries bad sectors up to three times.
• -d: Direct disc access, bypassing the kernel cache.

Step 3: Check the Recovered Disk

After the data recovery process is complete, it’s crucial to check the integrity of the recovered filesystem. Use the fsck command to do this:

sudo fsck -v -f /dev/sdc1

This command will verify the filesystem on /dev/sdc1 and attempt to fix any errors it finds.

Step 4: Mount the Recovered Disk

Finally, mount the recovered disk to access the data:

sudo mount /dev/sdc1 /mnt

If everything has gone smoothly, you should now be able to access your data from the /mnt directory.

Frequently Asked Questions (FAQs)

What is the purpose of the logfile in ddrescue?

The logfile records all the operations performed by ddrescue, including the sectors that were successfully copied and those that encountered errors. This allows you to pause and resume the recovery process without losing progress and provides a detailed record of the recovery process.

How long does the ddrescue process take?

The duration of the ddrescue process depends on the size of the disk and the extent of the damage. For heavily damaged disks, the process may take several hours or even days, especially if you set a high number of retries for bad sectors.

Can ddrescue recover data from a completely dead hard drive?

No, ddrescue cannot recover data from a drive that is completely dead or unresponsive. It is designed to recover data from drives that are partially damaged but still detectable by the system.

What should I do if fsck fails to repair the filesystem?

If fsck fails to repair the filesystem, you might need to use more advanced recovery tools or consult a data recovery specialist. In some cases, the filesystem may be too corrupted to recover using standard tools.

Conclusion

Data recovery is a critical task that requires the right tools and techniques. The ddrescue command is a powerful utility for rescuing data from crashed disks, especially when dealing with I/O errors or bad sectors. This guide has provided a comprehensive overview of how to use ddrescue to recover data from a failed disk on a CentOS 7 server and how to address common filesystem errors like the "wrong fs type, bad option, bad superblock" error.

Remember, while ddrescue is a valuable tool, it’s always best to have regular backups to minimize the risk of data loss. By following the steps outlined in this guide, you can recover your data and restore your system to normal operation.

Ensure you use the right mount options and keep your system updated with the necessary tools and programs to avoid similar issues in the future. Thank you for reading the huuphan.com page!