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RAID Data Recovery, how it works?


What is RAID?
The idea of a RAID is to store a large amount of data onto multiple disks with reasonable cost, therefore, the acronym “RAID" stands for Redundant Array of Inexpensive Disks.

What do we need to do to recover data from a RAID System? The data on a RAID array is striped all over the disks eg. if we have a 2Gigabyte Microsoft Exchange Mail Box Store File (priv1.edb) on 2 disks RAID-0 system then each disk of the 2 disks stores about 1 gigabyte of the that file, in this case recovering 1 disk out of 2 will not do the job because we will only be getting 50% of the file BUT NOT half of the file’s data!
Do you know why?
This is because usually the 2GB (EDB) file is not written in the sequence as (1,2,3) to the 1st disk and (4,5,6) to the 2nd disk.

A successful Raid recovery requires reading all the hard disks in the RAID set when recovering data from RAID0 or JBOD (Just a Bunch of Disks) or from 2 hard disks out of 3 in the case of RAID Level 4 or 5.

What are the common RAID Level 5 System failures? There are three common problems that occur with RAID-5 disk sets:
1 – Two or more hard disk drives went offline and the server no longer recognizes the RAID container.
This problem usually occurs when one or more of the disks have an external or internal physical malfunction such as a power circuit board failure or a head crash.
To solve this problem we would need to extract the data from as many as possible of the disks including the damaged disks, in most cases we would need to open one or more of the disks in our clean lab and perform sector-by-sector reading onto another disk.
2 – A RAID controller failure, replacing the controller with a new one did not do the trick!
This happens with some brands of RAID controllers where the RAID Array configuration is saved within the controller.
To recover the data, we would need to rebuit the RAID structure using a virtual RAID controller.
3 – An accidental RAID Rebuild has caused all the data to be lost!
This is one of the toughest tasks and many data recovery firms have no tools to reconstruct the original RAID.
To recover the data from this kind of situation we would need to take several sector range samples from all the disks and try to find what the original configuration was and how deep the new rebuilt went through, however, our firm is proud to announce that we have managed to recover data from more than 90% of these cases.

Why we are one of the most successful data recovery companies in Europe? Apart from the long years of experience (Data Recovery Direct was found in 1994 as part of Digiware Ltd) we always follow strict procedures when recovering data from RAID arrays, some of these procedures are:
1 – Take an image of each healthy drive and perform the data recovery on the disk copy NOT the original disks.
2 – We do not use any commercial data recovery software as they might cause more damage and make recovery impossible.
3 – We use special techniques to investigate through the disks to find what the actual cause of failure was before we carry out any data recovery process.
4 – We have a large internal knowledgebase of RAID problems and solutions and hardly to come across a problem that we have not came across before. Each job we receive is logged into our system from start to finish with all the technical information.
5 – All RAID recoveries are supervised by at least two technicians and any decision to take any step forward must be agreed by both technicians, this way, there is much less chance for human error on a client’s data!


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