When RAID failure occurs, data recovery from RAID can be very challenging.
However, it is not an impossible task. The recovery of data depends on a wide variety of factors.
For example, the level of the array plays an important part in its recoverability.
RAID level 0 is a striped array that has no fault tolerance. If one disk in this array goes down, all data becomes inaccessible. RAID level 1 is a mirrored array with fault tolerance.
If one of the mirrored disks fail, the data can usually be easily recovered from the other disk in the mirror.
In RAID level 5, the data is striped with parity. When one disk fails, the array is degraded but the data is still normally accessible. If two disks fail, then data becomes lost. It therefore becomes easy to see why the RAID level used impacts RAID recovery.
Another factor to consider is the condition of the hard drives in the array. Many times, there is nothing wrong with the disks and the problem is within the RAID configuration itself.
But most of the time, there are disk errors that cause the array to go offline. Disks in the array can have numerous problems including bad sectors, cyclic redundancy errors, and mechanical failure.
Signs of disk failure become evident with the presence of flashing lights on the server. Sometimes you can hear evidence of mechanical failure such as disk clicking. The recoverability of data depends on the condition of the problematic disks and whether or not they can be repaired.
Another factor that comes into play is whether the array was built with software or hardware. A software array is built within the operating system and does not use a disk controller.
A hardware array is built using a physical controller. Problems can occur with both hardware and software causing the array to fail.
When an array has failed, it is important to choose expert assistance for the recovery of data. Mistakes can cause data to be overwritten or deleted. It is also important to label the disks in the proper order and document events that occurred leading up to the failure and steps taken after the RAID failure.
Data recovery from RAID can be difficult, but it is not always impossible.
For a successful outcome, RAID recovery should always be performed by a professional data recovery company.