The re-establishment of data is with him with 's most interesting when there are the multiple exits to face, thus the combination of a failure of RAID with the removal of the files of a filesystem of UNIX UFS causes a re-establishment particularly provocant of data.
Fix the data
The first aspect of work is the fixing of the data. Any honourable company of re-establishment of data, and there is much, will religieusement fix religieusement all the available data before beginning any work. The work of phase on the discs of a RAID without initially to have fixed copies of image of each one, and risking the total loss of data should be there all the failures of material or the rebates, morally indefensible and is commercially moved. There are many tools available to the functioning discs of copy of image.
Define the RAID
There is no standard organization of RAID 5. RAID 5 described a method to bar data through a certain number of discs with creation of the data of parity XOR which are distributed through the discs.
The calculation of data of parity for RAID 5 is frank, but the order in which the discs are employed, the order in which the parity is distributed through the discs and the size of each storage block on each disc are not. It is where the method of UFS (and EXT3 and XFS) to divide a volume into groups of attribution is a great advantage. All the NTFS which you really obtain is the beginning of the MFT and the mirror of MFT, and there can be several organizations of RAID 5 which have as consequence the latter who are placed correctly, so much there is a great dependence at the time analyzing the filesystem to increase the process of analysis. With UFS there are a copy of the super-block followed by the tables of node of index and binary cards of attribution to the equidistant positions in all volume. This returns determining the configuration of relatively frank RAID in the majority of the cases of re-establishment of data of UNIX.
Analyze the data
After having established the organization of RAID the next challenge is to detect the data required. There is much which claims that the removed re-establishment of data of file of a volume of UFS is not possible, and there are good reasons for this complaint, but it is not entirely precise.
To start with we let us must consider the way in which UFS controls the attribution of the data for files. Each file is described by a node of index, it is where the information concerning of the dates and times of files, cuts and attribution are stored. Attribution is a certain number of indicators to the storage blocks which forms a file, plus some indirect indicators of block. When a file is removed the indode is free for the re-use and the information of attribution in it is removed. This means that there is no method to employ a program to sweep the nodes of index for the removed files in the manner which can be made by sweeping the entries of MFT of a filesystem of NTFS to take again files.
What is required is the knowledge of the files which must be recovered. The majority of the types of files have the information of identifiable heading, and for others there could be previous versions which can be found on supports for the comparison. Then an arrangement in the way is necessary in which the files are attribution under UFS and which additional structures are employed. Armed with this knowledge it is completely possible to recover a choice of the files though the primary information of attribution was removed.
Re-establishment of data of UNIX
This approach with the re-establishment of data of UNIX carried out some remarkable successes, but it would be erroneous to claim that the re-establishment of data was always feasible. For larger data files, for example databases, the level of success was high. For the filesystems which contain a great number of small files and where there was widespread removal of file the level of success is not usually also raised, particularly that without node of index for any file, unless there is a notation of the numbers of node of index, it will be never feasible to associate the recovered files the ones of with the names of file and directory.
Thus, rather than lodge the unworthy complaint that files can always be recovered, it is better to declare than they often can and than it is erroneous to decide that something is impossible until all the ways were explored.
The author had worked like an engineer and a programmer of software of re-establishment of data during the 25 last years RU, the USA, Germany and Norway and has now, with other skilled technicians of long time, started businesses of re-establishment of data
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