How to Recover Data from a Failed RAID5 Array? GP#KaTuts

Guest Post By Lizzy Smith

RAID, also known as Redundant Array of Independent Disks has proved to be a boon as it provides high performance to computer users, especially server users. Before heading towards further discussion, let us know a little more about RAID. RAID is a collection of many disks that are joined together to form an array. The combination of these disks provides an excellent fault tolerance feature and higher protection against data loss than a single hard drive. The overall advantage of RAID is that multiple disks work together to increase the overall system performance.

But sometimes, to a darker side, they may be very troublesome too.  While working on a RAID server, the user may face a sudden problem in the RAID 5 configuration due to many reasons. Things will go worse in this scenario and the users can suffer huge data loss. The data loss is also difficult as RAID data recovery is not an easy task.

RAID data failure:

In the case of RAID 5 failure, the user can be survived from data loss if one of the member disks has failed. But in the case of multiple disk failures there is zero chance of recovering the data. The other reasons may be operator error or controller failure.

The main advantage of RAID 5 is that even if one (and only one) of the drives fails but the others are working, there will be no data loss and wouldn’t cause multiple disk failure. But there is a case of rebuilding which can cause a serious problem. In this case, the controller rebuilds parity using incorrect array parameters and often results in drive failure.

As the feature of RAID 5 says that it can smoothly function even after one failed disk, but it may also happen that a wrong drive may be forced back online first. The RAID controllers have a “force online” function. This unintentional forcing back of the wrong disk results in entire array failure within no time.

Below mentioned are the reasons for RAID 5 failure:

• Malfunctioned controller
• Missing RAID partition
• Sudden power surge
• Virus attack
• Simultaneous failure of two drives
• Incorrect RAID volume configuration
• Forcing RAID 5 array back online with a failed drive

It is also important for a user to determine the parameters of RAID 5 configuration in order to recover the RAID data. The parameters are stated below:

• Number of disks in RAID 5
• Disk sequence
• Block size used in the array
• Parity pattern used in RAID 5

What you can do on your behalf:

• Shut your PC down immediately
• Use an alternative disk connection
• Use a genuine anti-virus software
• Ensure labeling cables and drive placements
• Always take a regulated backup and check them often to ensure they're being taken successfully but do not think of a RAID-5 as a data backup solution
• Never shuffle disk drives in different "slots" of the array
• Don't remove more than one disk drive at a time from its mounted position

Rules of RAID recovery: Get to know and jot down what you know about the original array configuration:

Hardware configuration: The member disks and controller ports and cables should be marked with a marker.

Logical RAID configuration: The logical RAID configuration includes the following parameters:

• RAID type
• Number of member disks
• Disk order
• Block size
• Start offset for the data on the member disks
• Parity pattern

Follow these steps to perform Data recovery from failed RAID 5 array

• Shut down the PC immediately. (As the two drives are already failed, there are possible chances that the RAID controller may further perform writes on the other disks-that have not failed, which may cause complete array failure and ultimately data loss)
• Immediately, rush to collect the needed hardware and software for RAID recovery (spare PC, NAS as an external storage). The external storage should have same size as the RAID disks. A UPS to prevent sudden power surge and an external HDD dock to attach failed RAID disks to a bootable Windows OS.
• Download Trusted RAID 5 data recovery software like Stellar Phoenix RAID Data Recovery.
• Disassemble the failed drives to identify them and note down the parameters of the failed disks.
• Run RAID recovery on the failed disks by using Stellar Phoenix RAID Recovery software.
• As the main screen appears, click RAID Recovery.
• After selecting the RAID 5 tab, select the hard drives to reconstruct RAID. (Take the help from the previously noted names/ numbers of the failed disks). Provide other features of the failed disks that you know. In case you don’t know, mention ‘Don’t know’.
• On clicking the ‘BUILD RAID’ button, see the RAID construction and select it.
• Now, navigate to the data recovery window by clicking on ‘Show Volume List’ button.
• Now there will be list of the volumes in the chosen RAID construction and can be chosen to perform data recovery operations.

On a final verdict, always be vigilant about the kind of power backup you are using, the antivirus you are keeping is genuine or not. Most importantly, always backup your RAID arrays because prevention is always better then cure. But in the most severe cases, keep a quality RAID recovery software like Stellar.