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Raid5 Data Recovery of the strange phenomenon - the logic of unimaginable
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HP server recently took over a four disk RAID5, which can not identify a physical disk, then mix with the other three disks to recover data, recover from data that is not normal, so think of ways to fix the piece of physical hard disk failure, but fortunately repaired a piece of physical failure of hard disk, the images do the work. so in accordance with the following steps: 1, the use of hard drive failure in RAID5 mirror combination, divided into 3 sub-combination of lack of data in a different hard drive; 2, the export of data originally have a problem, try to open, see if the file is normal. The result: No matter what a big piece missing, the combination of abnormal data is out, open all problems. With "escort" test 4 disk redundancy, there are redundant information does not meet the raid5 data. According to past experience, may be directly announced the resumption of failure. Suddenly remembered that I had long ago restored to a case similar to this case now. So by no shortage of disk combinations, the results surprising: out of the data can be restored to open! From this case is concerned, the idea is to start falling into Raid5 missing hard disk to rule out anomalous combination will certainly determine the trap of stale piece of plate. Let's analyze: 1,4-block disk Raid5, if four disk is good, with four combinations of data certainly offer no problem, lack of data in any combination of a disk is no problem; 2,4 block disk Raid5, if there was a big piece of data is not fresh, then we drive through the combination of lack of validation data, we can determine the piece of disk data is not new; 3, if the missing disk one by one combination, the data are not right, then we tend to give up the next recovery (which will appear at the beginning of a drive to take over when there are physical problems, we try to taste the rest of the hard drive to recover data combination If the data does not, we certainly have a big piece of data that is not fresh, but hard data is not fresh in the normal hard drive, when we had a good fix a broken hard drive later, we take the idea is to use the original bad disk in combination, a lack of original good disk, rather than to combine all of the hard drive, what we ignore this step) Formed in 4 Raid5 disk array, why do we offer a combination of lack of any data not on it? The combination of using all the data on the hard drive on it? Perhaps the data recovery industry, one encountered this problem, may also not thought to understand what is going on. After some thought I reached the following conclusions: XOR RAID card as the module does not work, or abnormal operation, resulting in the write data to the disk array, the data block is written successfully, but the redundant (check) block is not written successfully, or XOR operation to get a wrong result error Write parity block position, so we use tools to drive the XOR operator 4 results get a wrong result, we believe that one bad disk. Because the data blocks written to normal and the parity block error, so we can not use the lack of a way to combine disk, be sure to use the combination of all of the hard disk to restore the normal data.
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