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Principle of Raid5 data recovery algorithm

To understand the principle of raid5 data recovery, we must first understand raid5. "the independent disk structure of distributed parity", which is what we call raid5 data recovery, has a concept to understand, that is, "parity". We can simply think of it as an "XOR operation" in binary operations, and the commonly used logo is xor. The rule of operation is that if the values of the two are the same, the result is 0, and if the results are different, the result is 1.

For example, if 0101 xor 0010 is calculated according to the above operation rules, the first bit of both is 0, and the result is 0. If the values of the second, third and fourth digits are different, the result is 1, so the final result is 0111, which is expressed by the formula as: 0101 xor 0010 = 0111, so if one of them is missing in a xor breadc, we can calculate it from other data. This is the whole secret of raid5 data recovery. After knowing this secret, it will not be a problem for raid5 data to lose your own recovery data.

Raid5 data recovery case

In the case, the raid that needs data recovery is built on the POWEREDGE server, a total of 12 hard disks, a single disk capacity of 500g, the system platform is Linux platform, ext3 file system. Disk 1 and disk 4 in Raid report yellow lights on two hard disks. After checking, the manager made a mandatory online operation on disk 4. After the mandatory online operation, it was found that most directories could not be opened, and some files were lost in some directories that could be opened.

1. First of all, analyze the original raid structure, remove the No. 4 disk that is forced to go online, add the No. 1 disk, and build the raid platform through the virtual environment.

two。 Then the software is used to extract the auxiliary data, and the irregular bad track is found in the No. 1 plate after extracting the data.

3. We chose a commonly used mirroring tool to fully mirror the No. 1 hard disk, and more than 90% of the bad channels were read successfully.

4. Add the mirrored data to the virtual raid environment, extract the data again, and more than 99% of the data has been completely recovered.

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