Data recovery from RAID 5 arrays require advanced knowledge of how RAID 5 functions at the controller level. Block sizes, drive order and parity rotation and start offsets need to be calculated before even starting to search for lost data. Our engineers have developed software that calculates the required RAID 5 parameters in a matter of minutes. Considering the number of possible combinations, it can take hours and sometimes days just to calculate the correct information so that the data lines up properly. We have seen several cases where customers have come to us, for us to find out that other attempts had been using incorrect parameters, and we have managed to recover all data.
RAID 5 arrays require a minimum of three drives configured so the data is stored in stripes. In an array with 4 drives, each stripe contains 3 data blocks and a single parity block. For each stripe, the parity block 'rotates' to the next drive in the sequence. In the diagram below, you can see that in stripe 'A' parity is on disk 3, on stripe 'B' the parity has 'rotated' to Disk 2. Hence the term 'Striping with rotating parity'
RAID 5 is used for general purposes data. Because of the parity block in each stripe, it offers redundancy. If a single drive fails, the data is still accessible from the remaining drives in the array. Where hot spares are used, the system will automatically rebuild on detection of a drive failure. If a second drive fails, then the system will halt.
If you would like to talk to a RAID data recovery engineer about the problem with your system please phone free 0800 072 3282