When RAID failure occurs, data recovery from RAID can be quite challenging. However, it's no impossible task. The recovery of data depends upon a wide variety of factors.
The Level of the array plays a significant part in its recoverability. RAID level 0 is really a striped array that has no fault tolerance. If one disk in this array falls, all data becomes inaccessible. RAID level 1 is really a mirrored array with fault tolerance. If among the mirrored disks fail, the information can usually be easily recovered from another disk in the mirror.
In RAID level 5, the information is striped with parity. When one disk fails, the array is degraded but the information remains normally accessible. If two disks fail, then data becomes lost. It therefore becomes obvious why the RAID level used impacts RAID secure data recovery.
Another factor to think about is the situation of the hard drives in the array. Often times, there's nothing wrong with the disks and the thing is within the RAID configuration itself. But all the time, you will find disk errors that cause the array to go offline. Disks in the array may have numerous problems including bad sectors, cyclic redundancy errors, and mechanical failure. Signs of disk failure become evident with the clear presence of flashing lights on the server.
Sometimes you can hear evidence of mechanical failure such as for example disk clicking. The recoverability of data depends upon the situation of the problematic disks and if they may be repaired.