How to Recover Data from a RAID Array

A RAID is a storage technology that allows you to store large amounts of data with built-in security against data loss.  It does this by spreading the workload across multiple disk drives, so that if one fails, another can pick up the task.  Like most external storage solutions, RAIDs are available at multiple levels of power and efficiency, from small arrays suitable for small-scale video editing to powerful setups with vast amounts of storage and processing power.  RAIDs are designed to suffer as little as possible from crashes and data loss: data storage and processing are spread across multiple drives, and RAID software is designed to alert the user to bad drives immediately, so that they can be replaced with new ones before data becomes corrupted.  If you’re using a RAID, it usually means you’re pretty serious about your computing and data needs, and RAIDs are built to cause professionals as little headache as possible.

Of course, even the best hardware in the world isn’t immune to failure, and occasionally it happens that a RAID will not be able to distribute the workloads across its drives without using a bad one, causing data loss.  It is even possible for a RAID system to fail completely, which, given how much information is usually stored in a RAID, can result in catastrophic data loss.  Luckily, RAIDs are designed to be easy to fix as well as easy to run, so unless your RAID has been completely physically destroyed, there are strategies you can try to retrieve your data.

The below tips are giving you a few tips on how to recover data from a RAID array in an easy manner.

Stop writing data to the RAID immediately

With any data storage system, if a problem arises the most important thing to do is to stop using the system.  Certain types of software damage can cause corrupt data to spread every time new information is written to the drive; if the damage is hardware-based, continuing to send information across a bad connection can put stress on weakened materials and make it much harder to fix.  For the best chance at recovering your lost data, you need to immediately stop using the damaged RAID, even if it is still partially working.

Do not use your usual disk repair programs

Most computers have built-in systems that can repair minor damage to an internal or external hard drive, sometimes without much loss of data.  If you’re used to running these commands whenever something fails, it’s easy to use that as the first solution.  But RAIDs handle data very differently to most internal or external hard drive because of the way they spread data across multiple drives.  Running commands such as Windows’ chkdsk can interfere with the RAID’s own systems for restoring and backing up data, damaging your stored data and the RAID’s programming beyond repair.

Find and replace the damaged drive

Because RAID systems are built for redundancy, a RAID can function with one of its drives damaged.  As soon as you realize that one of the drives is not functioning properly, stop writing data to the RAID and figure out which drive is damaged.  Usually an indicator light on the RAID housing will show you which drive is damaged; otherwise you may be able to run diagnostics from your computer.  When you have identified the damaged drive, replace it with a new drive.  The process varies slightly depending on the manufacturer, so consult the manual carefully before replacing the drive.  Once the damaged drive has been replaced with a fresh one, you can tell the RAID to rebuild itself using the new drive, either using a driver from your computer, or by shutting down the computer and rebuilding directly from the RAID.  RAID systems are designed to rebuild using new drives without any loss of data, so if you’ve replaced the drive correctly, all you have to do is wait.  But be careful: even though replacing a drive is a relatively simple procedure, doing it wrong can cause the RAID array to fail completely.  If you have any doubts, stop what you’re doing and ask a professional to step in.

Use data recovery systems on the damaged drive

Once the damaged drive has been removed from the RAID, you can use usual data recovery systems to try to retrieve any data that wasn’t backed up within the RAID itself.  This may mean using a data recovery program, duplicating the drive to another hard drive using an enclosure, or taking the drive to a professional computer technician for data retrieval.  It is usually possible to retrieve data even from a damaged drive, but if not, as long as you replaced the drive and rebuilt the RAID correctly, your data loss should be very minimal.

Recovering data from a broken RAID

Perhaps counter-intuitively, recovering data from a RAID that is completely broken is much easier than recovering data from a RAID with one damaged disk.  Reconstructing a broken RAID is a lot like re-formatting an external hard drive: a third-party computer program can be used to wipe the RAID and re-build its programming completely to get rid of any software corruption.  Reconstructing a damaged RAID is a simple, repeatable procedure, but it’s important to back up all your data first.  Though it takes time and space, the most reliable way to back up your data is to create disk images of each of the RAID’s member disks, giving you an identical copy of each disk that is easy to restore once the RAID is repaired.  You can then use a third party RAID recovery program to reconfigure the member disks as standalone disks, and restore or reconstruct the data from each one individually.  Once the data has been safely reconstructed and backed up, you can take your RAID array to a professional to determine whether it can be safely fixed.  If the problem is hardware-based, it may be a simple matter of replacing a component; if the issues is with the RAID’s software, once your data is backed up you can try re-formatting the RAID array.  Despite that reconstructing a broken RAID is much easier than repairing a damaged drive, it’s still a good idea to take the RAID to a professional if you have any doubts: with terabytes of important data at stake, you should always consider data recovery first, and cost second.

by David Molnar

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