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\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;dd is a common Linux command for copying data by block size. It can also perform specified conversions while copying. However, what I am going to explain today is not the use of its conversion, but the use of it to help rescue a hard drive with zero tracks.

Probably the situation is this: There is a block of hard disk, divided into two partitions, the partition is a system partition, installed Windows XP; partition two is a data partition, stored a large number of data files. A few days ago, suddenly reported track 0 hard disk damage, MBR can not be read, due to MBR damage, resulting in the loss of the partition table, after the use of bad sectors detection, partition table repair and other tools to try to repair, are unsuccessful.

\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;Solution process: Partitioning is basically hopeless (bad roads are too much), and the data is not important. Considering the structure of the data stored on the hard disk, the data of partition 2 should still be normal, but the MBR cannot read and write normally. For this reason, I use dd to copy the data on it to another hard disk, and then repair the partition table. Finally, Successfully restored all data in Partition 2.

First, principle

The logical structure of the hard disk can be seen here:

In simple terms, MBR is responsible for managing partition information, but actual data such as file name, directory information, and file content are all under the actual disk sector after the partition address. This is why the partition table is damaged and the data is not lost after repair.

This time, my partition 2 was found but I couldn't write it into the MBR, so I had to use another hard drive.

Second, the solution process

1, bad hard disk situation

Before repairing, you need to make sure that the hard disk is broken there. Since it can be recognized in the BIOS, that is, the hard disk motherboard is normal.

※ Prerequisites for repair: To ensure that the data will not be damaged, be careful when repairing, do not overwrite the actual data, and do not perform any write operations on the original actual data.

Use the Deep Mountain Red Leaf Tool CD to start the PQMagic tool and report the following error:

After ignoring, see the following hard disk information, because can not accurately determine the size of the original partition, in order to ensure that will not affect the actual data, can not take the reconstruction of the partition.

Then, I tried to run the 'Partition Table Doctor' tool and I was unable to read the MBR:

After entering, click 'Rebuild Partition' to enter 'Interactive Mode' to find the previous partition:

Partition 2 can be found but the MBR table information cannot be saved:

At this point, the conventional method basically can't get the data of partition 2 out.

2, the repair process

Consider that Partition 2 is already available, and the actual data should be normal. (Because the bad is only the front part of the hard disk), so I thought of a solution.

Bring both hard drives to a machine, boot with a CD, for example linux rescue enters CD-ROM rescue mode and run:

Among them, hdc is a bad hard disk A, hda is a good hard disk B, and skips 80480 blocks, each block 1K. This is for security, I only copy by the size of 1K per block, so it is very slow. If you want to increase speed, you can increase the size of each block and calculate the number of skipped blocks.

Skip and seek indicate the number of skipped input and output blocks, respectively.

After the operation is completed, remove the bad hard disk A and use the 'Partition Table Doctor' on the dark red leaves to rebuild the partition table:

After saving, use PQMagic to see that partition 2 has been restored:

After the restart (requires restart to refresh the partition table information of Windows PE), the data accessing the hard disk is normal, and the work is completed.

Third, other

Based on the same principle, a cabinet was encountered in a project. Due to user misoperation, the partition of the cabinet was changed to the Sun OS format.

But after partitioning, there was no formatting work. At this time, the actual data in the cabinet is generally not lost.

Therefore, you can use dd to save part of the data information that needs to be modified:

That is, backup 1 GB of data, in case of problems, can be restored.

Then, use dd to remove Sun Label:

Finally, use fdisk / dev / sdb to rebuild the partition table according to the original size, save and mount, data recovery.

Related logs

[original] Asianux 4.0's rescue mode

[Original] Linux Magic Key - SysRq (R-E-I-S-U-B)

[turn]How to create a third-party drive

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